Slerj SSR-LC User manual

SSR-LC User’s Manual
Revision E
2 September 2019

SSR-LC User’s Manual
Rev E, 2 September 2019
© 2019 Slerj, LLC 2 www.slerj.com
CONTENTS
1Introduction ............................................................................................................................. 4
1.1 Description....................................................................................................................... 4
1.2 Features ............................................................................................................................ 4
2Getting Started......................................................................................................................... 4
2.1 Device Versions ............................................................................................................... 4
2.2 The SSR-LC Hardware .................................................................................................... 5
2.3 Connecting the SSR-LC................................................................................................... 6
2.4 Using the SSR-LC............................................................................................................ 9
3Functional Overview ............................................................................................................. 10
3.1 Serial Channel................................................................................................................ 10
3.2 Data Recording Subsystem ............................................................................................ 10
3.3 User Interface Module.................................................................................................... 13
3.4 Real-Time Clock............................................................................................................ 13
3.5 Digital I/O ...................................................................................................................... 13
4Interactive Shell..................................................................................................................... 14
4.1 System Commands......................................................................................................... 15
4.2 File Commands .............................................................................................................. 15
4.3 Device Configuration..................................................................................................... 16
4.4 Capturing the Shell......................................................................................................... 17
5Time Tagged Archives .......................................................................................................... 19
5.1 Data Packet..................................................................................................................... 19
5.2 Time Correlation Packet................................................................................................. 20
5.3 The STTP Utility............................................................................................................ 20
6Specifications......................................................................................................................... 20
6.1 Electrical......................................................................................................................... 23
6.2 Mechanical..................................................................................................................... 24
7Revision History.................................................................................................................... 25

SSR-LC User’s Manual
Rev E, 2 September 2019
© 2019 Slerj, LLC 3 www.slerj.com
© 2018 Slerj, LLC. All rights reserved
Reproduction in whole or in part is prohibited without the prior written consent of the copyright
owner. The information presented in this document does not form part of any quotation or
contract, is believed to be accurate and reliable, and may be changed without notice. No liability
will be accepted by the publisher for any consequence of its use. Publication thereof does not
convey nor imply any license under patent or other industrial or intellectual property rights. Slerj
assumes no responsibility or liability whatsoever for any failure or unexpected operation
resulting from misuse, neglect, improper installation, repair, improper handling, or unusual
physical or electrical stress including, but not limited to, exposure to parameters beyond the
specified maximum ratings or operation outside the specified range.
All brands and product names in this publication are registered trademarks or trademarks of their
respective holders.
SlerjTM is a trademark of Slerj, LLC.
Warranty
The SSR-LC Serial Data Recorder is warranted against defects in materials and manufacturing
for a period of 90 days from the date of purchase. In the event of a product failure due to
materials or workmanship, Slerj will, at its discretion, repair or replace the product. For
warranty service, return the defective produce to Slerj, shipping prepaid, for prompt repair or
replacement. Slerj, its suppliers, and its licensors shall in no event be liable for any damages
arising from the use of or inability to use this product. This includes business interruption, loss of
business information, or other loss which may arise from the use of this product.
SLERJ PRODUCTS ARE NOT DESIGNED, INTENDED, AUTHORIZED OR WARRANTED
TO BE SUITABLE FOR USE IN LIFE-SUPPORT APPLICATIONS, DEVICES OR
SYSTEMS OR OTHER CRITICAL APPLICATIONS. INCLUSION OF SLERJ PRODUCTS
IN SUCH APPLICATIONS IS UNDERSTOOD TO BE UNDERTAKEN SOLELY AT THE
CUSTOMER’S OWN RISK. Should a customer purchase or use Slerj products for any such
unauthorized application, the customer shall indemnify and hold Slerj and its officers,
employees, subsidiaries, affiliates, and distributors harmless against all claims, costs damages
and attorney fees which could arise.

SSR-LC User’s Manual
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© 2019 Slerj, LLC 4 www.slerj.com
1Introduction
1.1 Description
The SSR-LC is a low cost addition to the Slerj serial data logger product line. It records an
asynchronous serial channel at up to 230400 baud onto removable microSD media and provides
most of the advanced features of the 3-channel Slerj SSR-1. It is available in both 5V TTL
compatible and RS-232 versions. Streams can be recorded automatically at power up, on
command through a digital or PWM input, or using an interactive shell interface.
1.2 Features
Up to 230.4k baud recording
RS-232 or 5V TTL compatible (order option)
Powered from supply of 4.5–15 VDC or directly from 3.3 VDC
Small size: 1.40 x 1.10 x 0.20 inches (36 x 28 x 5 mm) (non-header version)
Supports microSD, microSDHC, and microSDXC cards
exFAT, FAT32, FAT16, and FAT12 file system support
Long File Name support
Support for raw and time-tagged recording
Battery backed real-time clock (with externally supplied battery voltage)
Flexible record control: digital input, PWM input, software controlled, or automatic
Interactive shell for configuration and file system operations
Flexible recording modes (overwrite/append, user defined path and file names, etc.)
2Getting Started
2.1 Device Versions
The SSR-LC is available in the following configurations:
SSR-LC-TS
S = no header (solder pads)
H = 14 pin header, dual row, 0.100 inch (2.54 mm) pitch
T = 5V TTL compatible (3.3V CMOS)
R = RS-232

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2.2 The SSR-LC Hardware
Figure 1. Top View (SSR-LC-TS shown)
Figure 2. Bottom View (SSR-LC-TS shown)
CAUTION: Like most electronic components, the SSR-LC can be damaged by
electrostatic discharge. Observe typical precautions for handling electrostatic
discharge sensitive devices.
microSD Card Slot
(push-push type connector)
Channel Status LED
Insert card as
shown in slot
beneath board.

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2.3 Connecting the SSR-LC
The pins of the main connector are described in Table 1. The SSR-LC is highly configurable and
has a variety of settings that can be changed through a shell interface (see Section 4 Interactive
Shell) and stored in on-board, non-volatile memory. Typical connections are shown in Figure 3
and Figure 4. In the default configuration (as shipped), the SSR-LC records when the
PWM/digital input command pin (PDI, pin 13) is connected to ground and the shell is not active
(pin 7 is allowed to float high). To access the SSR-LC interactive shell, tie pin 7 to ground.
Default serial parameters are 115200 baud, 8 data bits, no parity, and 1 stop bit. While the shell
is active (pin 7 is low), all received bytes goes to the shell and no data is recorded.
WARNING: SSR-LC-R device pins 9 and 10 are RS-232 voltage level compatible.
SSR-LC-T device pins 9 and 10 are 5 Volt tolerant, TTL compatible, 3.3V CMOS.
Do not connect an RS-232 device to pins 9 and 10 of an SSR-LC-T. Note that the
RS-232 compatible SSR-LC-R can be identified by the presence of an IC installed
on the bottom of the board at U4.
NOTE: A proper serial connection to the SSR-LC requires transmit, receive, and
ground connections. The ground connection is critical if the SSR-LC is powered
from a different supply than the device with which it is communicating.
Table 1. Main Connector Pins
Pin 1
ID
Description
1
Vs
Supply voltage (4.5-15 VDC, or 3.3 VDC 2)
2
GND
Supply return (tied to GND onboard the SSR-LC)
3,4
GND
Ground connection
5
3V3
Tied to the 3.3 VDC on-board supply
6
BAT
Battery voltage supply for the real-time clock
7 3
SH
Shell Select –interactive shell accessible when low
8 3
res
Reserved
9 4
RX
Asynchronous serial receiver input
105
TX
Asynchronous serial transmitter output
11,12
GND
Ground connection
13 3
PDI
PWM / Digital input record command
14 6
ST
Record status –High level indicates the device is recording
1See Section 6.2 Electrical for detailed electrical specifications.
2A 3.3 VDC supply can be used by connecting both the Vs and 3V3 pins to 3.3 VDC. If 3V3 is held at 3.3 VDC,
Vs must not be held at ground.
35V tolerant, TTL compatible, 3.3V CMOS input. Internally pulled up to 3.3 VDC.
4RS-232 compatible on SSR-LC-R. 5V tolerant, TTL compatible, 3.3V CMOS input on SSR-LC-T.
5RS-232 compatible on SSR-LC-R. 3.3V CMOS output on SSR-LC-T.
63.3V CMOS output

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Figure 3. Typical connections using a 4.5 to 15 VDC supply
Figure 4. Typical connections using a 3.3VDC supply
The jumper between +Vs (pin 1) and 3V3
(pin 5) is required when powering the
device from 3.3VDC.
Default command source is -dig. Pull PDI
down to record. Note that the device will not
record while SH is pulled low for shell access.

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Figure 5. Connections when configured with command source as +dig
The device can be configured to record automatically at power up by configuring command
source as +dig and connecting as shown in Figure 5. In this case, only the connections to the
power supply and the device to be recorded are required. Both PDI and SH have internal pull up
resistors (approximately 40kΩ), and will float high. With SH high (shell access not requested),
and PDI high with command source set to +dig, the device will begin recording at power up.
Note that the SSR-LC serial parameters (baud, data bits, parity, stop bits) must match the device
to be recorded.
The internal 40kΩ pull up resistors of the SSR-LC input pins may not be sufficient to keep the
pins high in electrically noisy environments. In those cases, it is recommended to use stronger
pull-ups (e.g., 4.7 kΩ) sourced from the on-board 3.3V supply (3V3, pin 5).

SSR-LC User’s Manual
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2.4 Using the SSR-LC
The SSR-LC is shipped in default configuration, with serial parameters set to 115200 baud, 8
data bits, no parity, and 1 stop bit. The device is configured to record when PDI is pulled low
and SH is high. The interactive shell is accessible through the serial interface when SH is low.
On power up, the SSR-LC displays a boot loader announcement and device details. If SH is low,
the shell prompt will be presented. A typical power-on sequence would produce output similar
to:
Details of the shell interface are provided in Section 4 Interactive Shell. As an example of shell
usage, consider changing the command source to +dig so that the device records when the PDI
pin is high. In the following sequence, <enter> means pressing the Enter/Return key to execute
the command in the shell. With the SSR-LC connected to a terminal program and the shell
active, type
config <enter>
to show the current SSR-LC configuration.
To change the command source to +dig, type
config src +dig <enter>
Verify that the configuration has been changed using:
config <enter>
To save the modified configuration in on-board non-volatile memory so that it is preserved
across power cycles, type:
config save <enter>
To confirm that the configuration has been saved, reboot the SSR-LC and verify configuration
using:
reset <enter>
config <enter>
Note that ‘cfg’ is an alias for ‘config’ and can be used as a shortcut.
Slerj Boot Loader v1.0.0
MK:Slerj
HW:SSRLC
MG:1662473
MD:SSR-LC
SN:1
SSR-LC Shell [Firmware 2.1.0]
>

SSR-LC User’s Manual
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3Functional Overview
The SSR-LC consists of an asynchronous serial channel, a data recording subsystem, a user
interface (shell) module, a real-time clock, and digital input/output for status and control.
Specific behavior for each functional element is defined by parameters that can be inspected and
modified using the user shell interface.
3.1 Serial Channel
The behavior of the serial channel is defined by the following parameters:
Baud rate –600 to 230400 baud, inclusive
Bits –8 or 7 (note that 7 bit frames require even or odd parity)
Parity –Even, odd, or none
Stop –1, 1.5 or 2 stop bits.
Echo –(Boolean) Echoes received characters out through the transmitter.
The single serial channel of the SSR-LC is attached to either the data recording subsystem or the
user interface module based on the level of the SH input pin.
3.2 Data Recording Subsystem
In addition to the basic serial channel parameters above, when a channel is attached to the data
recording subsystem (SH is high), several other configurable parameters apply:
Command Source
The Command Source parameter determines how the device is commanded to record.
Options include a discrete digital signal, a PWM signal, or software controlled through
the user interface module (shell). Command Source can be set to one of the following:
o-soft –The device records when the Soft Command parameter (defined in the next
major bullet) is true. With –soft, Soft Command is set to false at startup, and the
PDI pin is ignored.
o+soft –The device records when the Soft Command parameter is true.
With +soft, Soft Command is set to true at startup, and the PDI pin is ignored.
This selection for Command Source causes the device to automatically record at
startup.
o-dig –The device records when the PWM/digital input pin (PDI) is low.
o+dig –The device records when the PWM/digital input pin (PDI) is high.
o-pwm –Recording starts when the pulse width on the PWM/digital input pin
(PDI) is 1ms ± 250s. Recording stops when the pulse width on PDI is
2ms ± 250s.
o+pwm –Recording starts when the pulse width on the PWM/digital input pin
(PDI) is 2ms ± 250s. Recording stops when the pulse width on PDI is
1ms ± 250s.

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The PWM input is designed to work with the type of signal used by hobby servos. The
signal is considered valid when high going pulses are present with a pulse width between
750s and 2250s, and a period of 4ms to 65ms. The current record state for a channel
using the PWM input is changed only when a valid PWM signal is present that meets the
requirements of the selected PWM Command Source (+pwm or –pwm, specified above).
The PDI pin is 5 Volt tolerant and internally pulled to 3.3V. See Section 6.2 Electrical for
specifications.
Soft Command
Soft Command is a Boolean software parameter that is used when the Command Source
parameter is ±soft. When Command Source is ±soft and Soft Command is true, the
device records. The Soft Command parameter can be set through the user interface
module (shell).
File Type
The SSR-LC supports three archive types: raw, tagged line
1
, and time tagged archives.
oWhen file type is raw, bytes are written to file just as they are received, and no
timestamp information is attached to the data.
oWhen file type is tl (tagged line), text timestamps are inserted into the stream at
the first printable character following a newline or carriage return. This file type
is convenient for line-oriented data, but has a number of limitations as compared
to the time tagged archive. Since received data is modified with timestamp
strings prior to recording, the original data stream is not preserved. The
timestamp format is non-configurable, YYMMDDhhmmss.sss with a trailing
space. Since this mode adds 17 characters to every line received, it can
significantly inflate the volume of data that written to the card. A series of 4 byte
lines into the serial channel becomes a series of 21 byte writes to the card, and in
extreme cases (short lines at high speed) could exceed the write bandwidth of the
card. This mode is not appropriate for binary data.
oWhen the file type is tt (time tagged), bytes are encapsulated into an archive file
structure that associates a timestamp with each group of received bytes with a
resolution of 2ms. The time tagged archive format overcomes all of the
limitations of the tagged line format, but requires post processing to retrieve the
data. The archive is not intended to be human readable. A utility to perform the
post processing, STTP, is provided with source code. For details, see Section 5
Time Tagged Archives.
1
Support for tagged line archives was added in firmware 1.2.1.

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File Mode
Supported file creation modes are retry, overwrite, and append. When file mode is retry,
the SSR-LC will continue to retry the file creation operation until it succeeds. File
creation can fail if a file with the same name already exists. This mode is a useful
complement to user definable file paths (next bullet). Overwrite will cause an existing
file to be replaced by a newly commanded recording. Append will cause new data to be
appended to an existing file. For both overwrite and append modes, if the file specified
by File Path does not exist, it is created.
File Path
The File Path parameter holds a path template that specifies the name and location of the
file to be created when recording is commanded. A path template is a normal path string
that has replaceable fields defined in Table 2 below. A field is identified in the template
by a backslash followed by one of the field identifiers, or several consecutive identifiers
encapsulated in square brackets. For example, the path template /st[hms].dat would be
translated to the path /st083000.dat if the time is 08:30:00 when a file is created.
Similarly, the path template /gps/nmea\4.txt would be replaced by /gps/nmeaXXXX.txt
where XXXX is a number that is incremented on each attempt to open the file.
Currently, path templates of up to 29 bytes are supported, and the resulting path (with
fields replaced) must be no more than 64 bytes.
Table 2. Path Template Field Codes
Field
Identifier
Replaced With
Y
year [00-99]
M
month [01-12]
D
day [01-31]
h
hour [00-23]
m
minute [00-59]
s*
second [00-59]
t
tenth of second [0-9]
y
year (4 digit) [2001-2099]
X
hex digit month [1-C]
d
day of year [001-366]
2
two digit sequence number [00-99]
3
three digit sequence number [000-999]
4
four digit sequence number [0000-9999]
*This field identifier is lower case.
File Size
The SSR-LC supports automatic file close and reopen when a size (or time) threshold is
reached. Threshold values of 1 MB, 2 MB, 4 MB, 8 MB, 16 MB, 32 MB, 64 MB, 128

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MB, 256 MB, 512 MB, and 1024 MB are supported. Additionally, the File Size
parameter can be set to Hour, Day, or Week, causing new files to be started based on time
instead of size. By default, the File Size threshold is off, and no automatic close/reopen
operations are performed.
3.3 User Interface Module
The user interface module provides user access to file system operations, device status, and
configuration. More information on the interactive shell can be found in Section 4.
3.4 Real-Time Clock
The Real-Time Clock (RTC) maintains calendar time for the SSR-LC. An off-board backup
battery (typically Lithium 3V) connector to BAT and GND on the main connector allows the
RTC to keep time across power cycles. RTC time is used for file creation and received data
timestamps.
3.5 Digital I/O
Digital input and output lines are provided for hardware access to recording control and status.
On the main connector, PDI provides record control as discussed in Section 3.2, Data Recording
Subsystem. Additionally, a status line is provided (ST) to indicate when the channel is
recording. A bi-color (red and green) LED on the SSR-LC (Figure 1) provides status. The green
segment flashes to indicate reception of serial data on the channel and indicates when the shell is
active. The red segment illuminates solid red when the device is recording. The following LED
flash codes indicate device status.
Table 3. LED Flash Patterns
Status
Flash Pattern
Description
RECORDING
Red: Solid illumination
Device is recording (if shell is not active).
READY
Red: Short flash every 4 seconds
Indicates that a record channel is ready to
record when commanded.
CARD ERROR
Red: Long flash followed by two
short flashes every 2 seconds
Indicates that the card is missing or an
unrecoverable error has occurred.
CARD FULL
Red: Two long flashes every 2
seconds
Indicates that the card is full.
SHELL ACTIVE
Green: Solid every other second
with flashes during the off seconds
to indicate serial activity.
Indicates that the serial port is connected to
the user interface module instead of the data
recording subsystem. No data is recorded.

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4Interactive Shell
The interactive shell is designed to provide easy access to the SD card file system, device status,
and configuration options. Entering ‘?’or ‘help’at the command prompt provides information
about using the shell. Each command can be followed by ‘?’ to retrieve help information.
Multiple commands can be separated by a semi-colon. All commands are case sensitive. For
example:
The shell supports line editing and keeps a history of recently used commands. The ANSI
escape sequences shown in Table 4 are supported.
Table 4. Shell Line Editing Sequences
Keyboard Key
Alternate
Sequence1
Function
Up-arrow
^p
Recall the previous command to the command line.
Down-arrow
^n
Recall the next command to the command line. This is only
available when up-arrow has been used to recall a previous
command.
Home
^a
Move the cursor to the start of the command line.
End
^z
Move the cursor to the end of the command line.
Left-arrow
^k
Move the cursor left one character.
Right-arrow
^l
Move the cursor right one character.
Ctrl + Left-arrow
^b
Move the cursor left (backward) one word.
Ctrl + Right-arrow
^f
Move the cursor right (forward) one word.
1The caret (^) indicates use of the Ctrl key with the letter.
In the description of individual commands below, the following conventions are used:
[ ] indicates optional parameters
{ } identifies a set of choices separated by | (choose one)
< > indicates a variable defined in the help text
>cls ?
Usage: cls
Clears the screen.
Aliases: clear
>date;time
20130327
102840
>

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4.1 System Commands
System commands provide access to general system functions including the real-time clock and
operational status.
Table 5. System Commands
Command
Aliases
Description
cls
clear
Clears the screen.
date [yyyymmdd]
Sets the current date to the year, month, and day specified. If no
date is specified, this command returns the current date.
help
?
Provides help for using the shell.
reset
Performs a device reset.
status
stat
Displays device status (date/time, inputs, record channels).
time [hhmmss][ap]
Sets the current time using the hour, minute, and second specified.
The hour is assumed to be in 24 hour format. However, the time
may be appended with an ‘a’ or ‘p’ to explicitly identify AM or PM
if a 12 hour format is used.
4.2 File Commands
File commands provide access to the SD card file system. FAT12, FAT16 and FAT32 volumes
are supported, and long filenames are supported on FAT32. Many file system commands require
a path. Both relative and absolute paths are supported in the shell. Directories are separated by a
forward slash (/).
Table 6. File Commands
Command
Aliases
Description
chdir <path>
cd
Changes the current working directory.
del <path>
rm
Removes a file or an empty directory.
df
Prints the volume size and free space -.
dir [path]
ls
Lists the contents of a directory. If no path is provided, this
command lists the contents of the current directory.
mkdir <path>
md
Creates a directory.
pwd
Prints the current working directory.
ren <path1> <path2>
mv,rn
Moves or renames a file or directory from path1 to path2.
[NOTE: Do not move open files]
touch <path>
Updates the timestamp on a file or directory.
sz <path>
Send a file to the connected terminal2using the zmodem
protocol.
2
The zmodem file transfer has been tested successfully with several freely available terminal emulators, including
ExtraPutty, Teraterm, SyncTERM, and qodem.

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4.3 Device Configuration
Device configuration is manipulated through the user interface module. The current working
configuration is held in system memory (RAM) and can be saved to non-volatile memory for
preservation across resets. On startup, if the contents of the non-volatile configuration memory
are valid, the stored configuration is loaded and used by the SSR-LC. The shell provides access
to device configuration through the following commands:
Table 7. Configuration Commands
Command
Description
config
Prints the current configuration (including all channels).
config save
Saves the working configuration to non-volatile memory.
config load
Retrieves the stored configuration from non-volatile memory.
config erase
Erases the non-volatile configuration memory, but does not change the
current working configuration. When non-volatile configuration
memory has been erased, configuration defaults are loaded at startup.
config [args]
Provides access to serial channel and record parameter configuration.
If no arguments are specified, this command prints the current
configuration. Specific configuration commands are in Table 8.
config leds1{on | off | onx}
Allows the on-board LEDs to be turned off for power savings. The
onx option causes the LEDs to be active for 10 seconds after power is
applied.
1Option added in firmware 2.1.0
In addition to the global configuration commands presented in Table 7, there are several serial
channel and record parameter configuration commands. The commands in the following table
are entered as part of a command line ‘config command’.
Table 8. Channel Configuration Commands
Command
Alias
Description
baud <rate>
Sets baud to rate (600 to 115200).
bits1{8 | 72}
Sets data bits to 8 or 72.
parity { E | O | N | e | o | n }
Sets parity to even, odd, or none.
stop { 1 | 1.5 | 2 }
Sets the number of stop bits.
echo <bool3>
Enables echoing of received characters.
source [{ + | - }]4{ soft | dig | pwm }
src
Sets the command source.
soft <bool>
Sets the soft command parameter.
file type { raw | tl | tt }
Selects between raw, tagged line, and time-
tagged archives.
file mode { retry | append | overwrite }
Sets the channel file mode.
file path <path>
Sets the channel file path template to path. See
Section 3.2 Data Recording Subsystem for
more information on path templates.

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Command
Alias
Description
file size { off | 1 | 2 | 4 | 8 | 16 | 32 | 64 |
128 | 256 | 512 | 1024 | hour |
day | week }
Sets the file size threshold. See Section 3.2
Data Recording Subsystem for more
information on file size thresholds.
1Option added in firmware 2.1.0
2The SSR-LC does not support 7 data bits with no parity. A 7 bit data frame must have parity enabled.
3bool denotes a Boolean expression, and may be specified using
{ y | Y | t | T | true | yes | on } for affirmative and { n | N | f | F | false | no | off } for negative.
4The { + | - } prefix is optional. If not specified, + is assumed.
Note that multiple channel configuration commands may be specified together. For example, to
set the baud, parity and stop parameters with a single command, type
config baud 38400 parity N stop 1
Also note that the file option commands are two-word commands (don’t omit the word ‘file’).
For example, to set the file type to raw, type
config file type raw
4.4 Capturing the Shell
To allow access to configuration without knowing the current serial channel settings, the shell
can be captured by the user during startup. The feature is inherited from the SSR-1, where it is
necessary when all channels are configured for recording. For the SSR-LC, it is useful only if
the current channel settings are unknown. The capture mechanism operates prior to loading
stored configuration data, so the serial port always operates at 115200 baud, 8 bits, no parity, and
1 stop bit for capture.
The process for capture involves presentation of the boot loader message at startup, the user
quickly typing the string config, the device replying with an upper case, four character challenge
string, and the user echoing the challenge string back to the device in lower case. Details are as
follows:
On startup, the SSR-LC displays the boot loader message and device information.
An 800ms window begins in which a valid character of the capture sequence must be
received from the user. If an invalid character is received, or 800ms elapses, the capture
sequence is aborted and the device boots normally according to its stored configuration.
Each valid character received resets the capture window to 800ms. Since it is difficult to
judge the time from power on until the device is ready to begin receiving the capture
sequence, the valid capture sequence includes up to 5 lower case zcharacters prior to the
string config. A typical capture will involve hitting zwhile powering on the device until
the zcharacter is echoed from the device, then typing config.
When the previous step has been completed, the SSR-LC will send a random challenge
string consisting of 4 upper case characters, and a new capture window of 5 seconds is

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established. The user must type those same characters in lower case to complete the
capture process. If the challenge string is not answered in 5 seconds, the capture process
is aborted and the SSR-LC starts normally.

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5Time Tagged Archives
Often, it is important to know not only what serial data was transferred, but when it was
transferred. This is useful in both the analysis of communication systems and in the ability to
reconstruct streams as they originally occurred. The SSR-LC supports time tagged archives, in
which received bytes are tagged with the time they were received. When the device is
configured to record time tagged archives, the received bytes are encapsulated in packets prior to
being written to the file system. Two types of packets are currently defined: the data packet and
a time correlation packet. All multi-byte words in the archive are big endian.
5.1 Data Packet
The data packet uses the system free running clock as the time stamp source. Bytes are grouped
into 2ms windows for stamping. Each data packet begins with a base time stamp that identifies
the whole second in which the data was collected. The base time stamp is followed by a series of
frames that are composed of an incremental time stamp (fractional second within the base time
stamp window) and a group of bytes that were received during the increment. The data packet is
terminated by a checksum.
Table 9. Time Tagged Data Packet
Element
Bytes
Description
Packet Header
0x82 0xA2
2
Packet start sequence.
Run Time
4
Current run time in seconds.
Frame repeated until an mSec_Count value of 0xFFFF is encountered.
mSec_Count
2
Fractional second and number of bytes for this frame.
bits 15-7: milliseconds / 2
bits 6-0: number of bytes to follow (n)
Data
n
The nbytes that were received in the time window leading up to this
packet frame.
End Sequence
2
0xFFFF (invalid mSec_Count)
Checksum
2
Fletcher checksum calculated between Run Time and End Sequence,
inclusive.
Note that a software utility, including source code, is provided at slerj.com for parsing time
tagged archives into a variety of useful formats. See section 5.3 The STTP Utility for details.

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5.2 Time Correlation Packet
The time correlation packet associates the free running clock timer with the real-time clock. A
time correlation packet is written when the recording is started, every 10 minutes, and as the
recording is stopped.
Table 10. Time Tagged Time Correlation Packet
Element
Bytes
Description
Packet Header
0x82 0xA3
2
Packet start sequence.
Run Time
4
Current run time in milliseconds.
RTC Time
6
Real-Time Clock
word 0:
bits 15-4: year (2001 –2099)
bits 3-0: month (1 –12)
word 1:
bits 15-11: day (1 –31)
bits 10-6: hour (0 –23)
bits 5-0: minute (0 –59)
word 2:
bits 15-10: second (0 –59)
bits 9-0: milliseconds (0 –999)
Checksum
2
Fletcher checksum calculated between Run Time and RTC Time, inclusive.
5.3 The STTP Utility
The SLERJ Time Tagged Parser is a Windows command line utility (sttp.exe) provided with the
SSR-LC to parse time tagged archives into various output types. Source code is provided under
a non-restrictive (MIT) license so that it can be freely modified and incorporated into user
applications. The utility has a number of functions including the ability to extract the raw data
(without timestamps), extract line-oriented data prepended with configurable timestamps, extract
only portions of the data in intervals or windows, and extract text representations of the packets
stored in the archive. For more details on line-oriented extraction, see Application Note AN002
–STTP Timestamped Lines.