Tait T2000-A75 User manual

T2000-A75 Modem
Operation Manual
© Tait Electronics Limited
Corporate HQ: PO Box 1645, Christchurch,
New Zealand.
Tel: [phone]
Fax: [phone]
Web: www.taitworld.com/
November 2001
M2256-000-00-051

Contents
Section Title Page
1Overview 5
RS232 Interface 6
Compatibility 6
A75 Configuration 7
Command mode 8
Transparent mode 8
2Changing Modes 9
3Transparent Mode Operation 11
Transparent Mode effective data rate calculation 11
Transparent Mode RTS/CTS Signalling 13
4Command Mode Operation 17
Message Format 17
Calculating the [CHECKSUM] 18
Sending and Receiving Short Data Messages (SDM) 19
5Commands 23

November 2001 M2256-000-00-051 5
1 Overview
The CCDI (Computer Controlled Data Interface) is a command protocol embedded in the
T2000-A75 (A75) modem firmware to control the T201X radio.
The A75 is fitted to a T201X radio and is connected to a personal computer (PC) by a serial line
using five standard RS232 signals (TXD, RXD, CTS, RTS and GND).
The A75 can operate in two modes: Command mode and Transparent mode. In Command
mode, the A75 is controlled by the PC sending command sequences and receiving responses.
In Transparent mode there is a direct link between the PC and the FFSK modem on the A75
Modem board and the PC sends and receives data without having to pass messages using
CCDI commands. Transparent mode can be set to either 9600, 4800, 2400 or 1200 baud
between the PC and the A75. The over-air data rate is either 1200 or 2400 baud.
The T2000-A75 modem described in this manual is CCDI version 2.0 compatible. When an
A75 is retrofitted to a T2000 radio, some hardware modifications are needed. Refer to the A75
fitting instructions for details.
DTE
COM
Port
COM
Port
PC
PC
T2000-A75
(A75)
CCDI
capable
Modem
T201X T201X
or
Tait Orca
DB9
RS232 RS232 PCPC
CCDI CCDI

6 M2256-000-00-051 November 2001
RS232 Interface
The RS232 communication between the PC and the A75 has the following parameters which
are fixed in the A75 firmware.
For every byte sent, there are 10 bits sent including the start and stop bits:
• Number of data bits = 8
• Parity = none
• Number of start bits = 1 (set to ‘1’)
• Number of stop bit = 1 (set to ‘0’)
The RS232 D-Range socket at the rear of the T201X radio has the following configuration:
Note: The start and stop bits are removed by the A75 for the over-air transmission of data. The FFSK
data sent is pure binary 8 bit data only.
Compatibility
T201X Radio Firmware
When programming the T201X radio firmware for use with the A75 and CCDI, use version 3.01
or greater.
T2000 PGM
When the A75 modem board is fitted, the T201X PGM program settings have the following
constraints:
• ‘BCD Channel Selection’ should be enabled and polarity set to Normal so that the A75
can change the channel with the GO_TO_CHANNEL command.
• Economy mode reduces the radio’s power consumption when it is idle. When economy
mode is active and there has been no valid activity on a channel for the duration of the
economy mode timer, the radio begins economy cycling. This means that the beginning
of a transmission may be lost if it is received after a period of inactivity.
If ‘Economy mode’ is enabled in a T201X with an A75 fitted, set the default Transparent
mode Lead In Delay to 200 ms.
If a faster data transfer rate is required, then the Lead In Delay can be reprogrammed as
low as 40 ms, but the Economy mode must be disabled.
Connections Function Connections Function
1 Not used 6 Not used
2RXD7 RTS
3TXD8 CTS
4 Not used 9 Not used
5GND

November 2001 M2256-000-00-051 7
A75 Configuration
The A75 is configured for both Command and Transparent mode communication using the
PROGRAM command. It contains 18 ASCII hex characters and sets up the following parame-
ters:
• Transparent mode baud to either 1200, 2400, 4800 or 9600 baud
• Power-up default to Command or Transparent mode
• Command mode baud to either 9600 or the same as Transparent mode
• CTS and RTS signalling attributes
• whether the A75 sends an SDM Auto ACK after receiving an SDM; and waits for an
ACK after sending an SDM
• the Delay Time between receiving an SDM and returning an SDM Auto ACK
• the time that the A75 will wait for an SDM Auto ACK before sending a PROGRESS
message
• The Transparent mode Lead In Delay time. When the T201X radio receives serial data it
keys-up the transmitter but only starts to send the FFSK data after the Lead In Delay.
• The T201X Power-up channel
• The eight character Data ID assigned to the radio for receiving SDM data.
Refer to the PROGRAM command for detailed information.

8 M2256-000-00-051 November 2001
Command mode
In Command mode, the PC sends command sequences to the A75 and waits for a prompt before
beginning the next transaction. The A75 sends a prompt character ‘.’ to the PC to indicate that
it is ready to accept a new command. Some commands require the A75 to send a CCDI message
in response, before it sends the prompt.
Messages directed to the A75 will always be responded to, either by a return message, or by the
presence of the prompt.
Messages from the A75 are either solicited or unsolicited. Solicited messages are sent in re-
sponse to commands from the PC. Unsolicited messages such as PROGRESS or ERROR mes-
sages are sent by the A75 if there is a significant change in the state of the T201X that the PC
should be aware of. When errors are detected, an unsolicited ERROR message is sent by the
A75 to the PC. The A75 does not send messages that require a reply.
Transparent mode
Transparent mode creates a direct link between the PC and the FFSK modem located on the
A75. The transparent link allows the PC to send and receive data without having to pass mes-
sages using the CCDI Command mode.
The transparent link is administered by the A75 which reads FFSK data arriving from another
FFSK modem and sends it to the serial port. Any form of binary data is acceptable but the escape
sequence to switch back to Command mode should be avoided. The escape sequence character
is set to ‘+’ by default, or defined within the TRANSPARENT command.
PROGRESS messages are unsolicited status messages sent by the A75 but can be filtered out
in Transparent mode by enabling TMODE Filter control with the FUNCTION command. When
the TMODE filter is enabled, progress messages are not sent by the A75. When a PROGRESS
message is sent in Transparent mode, the escape character is attached to the front of the mes-
sage, e.g. zzzp0207C7 where ‘z’ is the escape character.
In Transparent mode, the A75 does not generate or detect CRC checksum data. However if a
SDM message is transmitted or received then the CRC checksum data is used.
Transparent mode serial baud can be set to either 9600, 4800, 2400 or 1200 baud using the PRO-
GRAM command.

November 2001 M2256-000-00-051 9
2 Changing Modes
In order to change from Command mode to Transparent mode, the PC must send a TRANS-
PARENT command to the A75. Once acknowledged, any further communication is linked di-
rectly to the A75 modem in Transparent mode.
When the TRANSPARENT command is sent to the A75, the escape sequence character that is
used to return to Command mode is also sent.
The escape sequence consists of a 2 second idle time, followed by three escape characters (with-
in 2 seconds), followed by a further 2 second idle time.
If the T201X defaults to Transparent mode at power-up, the escape character is set to the default
value of ‘+’.
Example
1. t is the message [IDENT] for a TRANSPARENT command telling the A75 to go into Trans-
parent mode
2. The [SIZE] parameter in this example is 01 as there is one character of data to follow in the
[PARAMETERS] field.
3. z is the escape character in the [PARAMETERS] field. When 2 second idle + zzz +
2 second idle is detected in Transparent mode, the A75 is forced back to Command mode.
4. The [CHECKSUM] in this example is B1. Refer to the Calculating the [CHECKSUM] sec-
tion for details.
(2s idle) + zzz + (2s idle)
Transparent
mode
Command
mode
tz[SIZE] [CHECKSUM]
PC(1) A70(1)
A70(2)
or Tait Orca
RS232 over air
PC(2)
RS232
‘.’
‘.’

10 M2256-000-00-051 November 2001

November 2001 M2256-000-00-051 11
3 Transparent Mode Operation
The Transparent Mode transmission format is as follows:
The default Transparent mode Lead In Delay is set to 200 ms. If a faster data rate is required the
Lead In Delay can be reprogrammed to a minimum of 40 ms using the PROGRAM command.
Note that if the Lead In Delay is set this low, Economy mode must be disabled.
The Tail Time of 20 ms is fixed in the A75 firmware.
Transparent Mode effective data rate calculation
The Transparent mode effective data rate is dependant on the amount of data sent in one trans-
mission. The more data is sent, the better the data rate.
Example
If we assume that 1K bytes of data is sent with a Lead In Delay of 200 ms:
Time to send data message + block head for each block of data
= ((( 1000 + ( 22 x 6 )) x 8 /1200 ) x 1000 = 7546 ms
Where:
1000 = bytes of data (1K bytes)
22 = (1000 bytes/46 bytes per data block) + 1 block to round up to the nearest block
= number of block heads
6 = bytes per block head (2 bytes for PREAMBLE + 2 bytes for SYNC + 2 bytes
for block LENGTH)
therefore:
(22 x 6) = total bytes in the block heads
8 = bits per byte
1200 = bits per second (bps) over-air standard baud
1000 = to convert bps to ms
Lead In Delay and Tail Time = 200 + 20 = 220 ms
Total time = 7546 + 220 = 7766 ms
Effective data rate = 10000 (bits) / 7766 (ms) = 1287 bps
If 1M byte of data is sent, the effective data rate goes up to 1500 bps.
Lead In
Delay
(200ms)
First block
(maximum 46
bytes)
. . . . . . . . nth block
(maximum 46
bytes)
Tail Time
( 20ms)
Preamble Sync Length data block
(maximum
46 bytes)
dummy CRC
(00)
Block Head

12 M2256-000-00-051 November 2001
Transparent mode Lead In Delay
The Lead In Delay time ensures that data is not lost from the front of the data block while the
transmitter keys-up. To achieve this, CTS inhibit is set to ‘0’ so that radio does not receive any
serial data from the PC during the Lead In Delay.
The Lead In Delay time can also be used to activate a series of repeaters in some common ap-
plications. When data is detected at the input buffer of the radio, the following chain of events
occurs:
1. the transmitter keys-up
2. a carrier is sent from the radio transmitter
3. if the receiving Base Station is set in Repeater Mode, the carrier is detected and Rx Gate
becomes active which in turn makes the PTT line active
4. the active PTT line keys-up the transmitter
This sequence is repeated with as many Base Stations as are in the chain.
The optimum length of the Lead In Delay depends on the number of Base Stations that need to
be activated before any data is sent.

November 2001 M2256-000-00-051 13
Transparent Mode RTS/CTS Signalling
RTS and CTS signals only operate when the A75 is in Transparent mode. The A75 can be used
with or without the RTS and CTS signals as determined by data rate considerations.
Transparent Mode data rate considerations
The A75 has a 50 byte Serial Input buffer and 54 byte Serial Output buffer.
• The PC baud is set up in the
terminal program.
• The A75 baud of 9600,
4800, 2400 and 1200 baud
is set using the PROGRAM
command. It must be set to
the same as the PC baud
rate.
• The FFSK over-air baud of
1200 or 2400 baud is set
using the PROGRAM com-
mand.
PC
Terminal A70
1200
baud
1200
baud
1200
baud
lead in
delay
RS232 over air
9600
baud
9600
baud
1200
baud
lead in
delay
(constant)
(constant)
A70
or Tait Orca
Example:
Example:

14 M2256-000-00-051 November 2001
RTS (Request to Send) Signal
RTS is an active high input signal to theA75 from the PC and is used to reduce data transfer
delays and improve data throughput.
RTS Inhibit is either inhibited or not, using bit 6 of the [ITEM1] parameter in the PROGRAM
command which configures the A75.
If ‘Inhibit RTS Signal’ is set to ‘1’ (RTS inhibited), then an RTS signal is ignored by the A75
(RTS off). When RTS is disabled, the A75 starts to transmit when data is received until the input
buffer becomes empty. Once empty, the A75 will stop transmitting after the Tail Time set in the
A75 firmware. Each time the transmitter keys up, it must wait for the Lead In Delay before data
transfer can commence.
If ‘Inhibit RTS Signal’ is set to ‘0’ (RTS not inhibited), when an RTS signal is detected (RTS
on) the following sequences can occur depending on the structure of the data.
If RTS turns off, the A75 will continue to transmit until the buffer is empty, and stops after the
Tail Time.
If the buffer becomes empty while RTS is still on, the A75 continues to transmit until either RTS
turns off,
or after the Tail Time if this occurs after RTS has turned off.
Time
data
buffer
empty
Tail
Time
RTS Inhibit=1
A75 PTT Tx
Lead In
Delay
Time
RTS on
data
RTS off
A75 PTT Tx
buffer
empty
Tail
Time
RTS Inhibit=0
Time
RTS on
data
RTS off
A75 PTT Tx
buffer
empty
Tail
Time (1)
RTS Inhibit=0
Time
RTS on
data
RTS off
A75 PTT Tx
buffer
empty
RTS Inhibit=0
Tail Time (2)

November 2001 M2256-000-00-051 15
If the data stream has a gap, while RTS remains on, the A75 continues to transmit. This elimi-
nates the data delay caused by the Lead In Delay at the start of each transmission.
If a long data stream is sent, the A75 continues to transmit, but the T201X stops transmitting
after the transmitter time-out. The transmitter time-out is set by the Transmit Time Duration
which is set to a default of 60 seconds in the T2000 PGM programming software.
If the radio transmitter times-out in this way, it can not transmit data again unless RTS is turned
off then on again.
Time
RTS on
data
buffer
empty
RTS Inhibit=0
gap
A75 PTT Tx
Time
RTS on
data
A75 PTT Tx
Tx Time Duration
T2000 Tx
Time
RTS on
data
A75 PTT Tx
Tx Time Duration
RTS off RTS on
data

16 M2256-000-00-051 November 2001
CTS (Clear to Send) Handshaking
CTS is an active high output signal from the A75 to the PC and is used to prevent data over-
flow under certain conditions such as a full input buffer. CTS should always be used if the PC
and A75 baud is higher than the over-air baud.
If the data throughput rate is small enough (less than 40 bytes in one transmission), then inde-
pendent of the baud, CTS handshaking is not necessary. If the data throughput is greater than
40 bytes in one transmission, CTS must be used to avoid data loss. This assumes a short lead in
delay otherwise the output data will overflow. At a low baud, 300 ms is a short Lead In Delay
but a higher baud may need a Lead In Delay as low as 40 ms.
The CTS state is controlled using bit 6 of the [ITEM1] parameter in the PROGRAM command
which sets up the configuration of the A75.
If ‘Inhibit CTS Signal’ is set to ‘1’, then the CTS signal from the A75 is always on (CTS hand-
shaking off).
If ‘Inhibit CTS Signal’ is set to ‘0’, CTS deactivates under the following conditions
• during the Lead In Delay
• if the PTT is pressed
• if the input buffer exceeds 34 bytes from a total 50 byte input buffer
If the PC terminal application continues to send data while the CTS line is off, the data will con-
tinue to be stored in the 50 byte input buffer.
When the buffer is full, further incoming data is lost until there is room in the input buffer again.
CTS will turn on again when the buffered data drops below 40 bytes.
At all other times the CTS is ON (high at PC end).
Data Quantity A75 and PC Baud Lead In Delay CTS Handshaking
<40 bytes / transmission 1200 (2400) - 9600 short not required
>40 bytes / transmission 1200 (2400) - 9600 short required

November 2001 M2256-000-00-051 17
4 Command Mode Operation
Message Format
All Command mode message packets take the general form:
[IDENT] [SIZE] [PARAMETERS] [CHECKSUM] <CR>
• All characters in a message are printable ASCII.
• Where numeric values are represented in ASCII-hex notation (two characters per byte),
characters A to F are upper case.
• The minimum length of a command packet is 5 characters. For example q002F is the
QUERY command where [SIZE] = 00 as there is no [PARAMETERS] field required.
• The maximum length of the [PARAMETERS] field is 42 characters. The maximum length
of the command packet is therefore 47 ([SIZE] = 2F) characters.
Example
#12C401060A010000BASE8F
1. # is the message [IDENT] for a PROGRAM command.
2. 12 is the parameter [SIZE] as there are 18 characters of data to follow in the [PARAME-
TERS] field.
3. C401060A010000BASE are the data bytes in the [PARAMETERS] field.
4. 8F is the calculated checksum of the message line.
5. The actual data that is sent out the port in hexadecimal form is:
23 31 32 43 34 30 31 30 36 30 41 30 31 30 30 30 30 42 41 53 45 38 46
Field Description
[IDENT] The message identifier. Identifiers are single ASCII characters (lower-case alphabetical)
which categorise the message type.
[SIZE] The number of characters which make up the [PARAMETERS] field. [SIZE] is an 8-bit
number expressed in ASCII-hex notation (two characters).
[PARAMETERS] An optional field, depending upon the command. Parameter values are generally character
strings unless explicitly stated otherwise. Parameter type is dependent upon the command
- there is no explicit type definition.
[CHECKSUM] An 8-bit checksum of the [IDENT], [SIZE] and [PARAMETERS] fields. Expressed in two
character ASCII-hex notation.
<CR> The carriage return packet terminator.

18 M2256-000-00-051 November 2001
Calculating the [CHECKSUM]
[CHECKSUM] is calculated by applying the following algorithm:
1. Take the modulo-2 sum of all message bytes preceding [CHECKSUM].
2. Retain bits 0 to 7, discarding any higher order bits resulting from the summation.
3. Form the two’s complement of the remainder.
4. Convert the binary number into two ASCII-hex digits, MSD first.
Example
#12C401060A010000BASE8F
1. Take the modulo-2 sum of all message bytes preceding [CHECKSUM].
• # = 23h, 1 = 31h, 2 = 32h, C = 43h etc. therefore the modulo-2 sum is:
23h + 31h + 32h + 43h + 34h + 30h + 31h + 30h + 36h + 30h + 41h + 30h + 31h + 30h
+30h + 30h + 30h + 42h + 41h + 53h + 45h = 471h
2. Retain bits 0 to 7, discarding any higher order bits resulting from the summation.
• 71h
3. Form the two’s complement of the remainder.
• 71h = 0111 0001
two’s complement = 1000 1111
4. Convert the binary number into two ASCII-hex digits, MSD first.
• 1000 1111 = 8F

November 2001 M2256-000-00-051 19
Sending and Receiving Short Data Messages (SDM)
A SDM can only be sent in Command mode from a PC but can be received in both Command
and Transparent modes.
Sending SDMs
In the examples shown, the first two bytes of the [PARAMETERS] field are set to FF which
translates to an SDM Lead In Delay of 5.1 seconds. The next eight bytes (12345678) are the
SDM Data ID of the radio receiving the SDM. The SDM text is ‘Hi’.
If the SDM data includes a SDM [MESSSAGE] parameter, the SDM text (‘Hi) will update the
SDM text buffer in the A75 EEPROM. If there is no SDM [MESSSAGE] parameter attached,
the buffer will not be cleared but retains its current contents
When an SDM is sent (➀), the T201X radio keys its transmitter immediately, and the SDM is
sent by the A75 after the SDM Lead In Delay.
SDM Auto ACK is either enabled or disabled when the modem is configured. This is done in
the A75 with the PROGRAM command or in the PGM programming software for the Tait Orca.
If the A75 has SDM Auto ACK is set to ‘1’ (enabled) in bit 7 of the [ITEM1] parameter of the
PROGRAM command, then:
• when the A75 receives an SDM, it returns an ‘ACK’
• when the A75 sends an SDM, it starts the SDM Wait for ACK timer
In the above example, the receiving modem A75(2) has the SDM Auto ACK disabled so no
‘ACK’ is returned. After the SDM Wait for ACK time, the A75(1) generates a PROGRESS
message (➁) of [PTYPE] SMD ACK (1D) with the flag set to ‘0’ (No ACK Received). Refer
to the PROGRESS command details for further information.
SDM
Wait for
ACK
Time
RS232 over air RS232
2
p 1D0 [SIZE] [CHECKSUM]
PC(1) A75(1)
A75(2)
or Tait Orca PC(2)
1Lead In
Delay
s FF12345678Hi [SIZE] [CHECKSUM] SEND_SDM
PROGRESS
Auto ACK = 1 Auto ACK = 0
PROGRESS
Wait for ACK triggers
PROGRESS

20 M2256-000-00-051 November 2001
In the example above, the receiving modem A75(2) has the SDM Auto ACK enabled so an
‘ACK’ is returned to the A75(1). When the A75(1) receives the ‘ACK’, it generates a
PROGRESS message (➁), of [PTYPE] SMD ACK (1D) with the flag set to ‘1’ (ACK Re-
ceived). Refer to the PROGRESS command details for further information.
If the A75(1) has SDM Auto ACK enabled and the ACK is not received after the SDM Wait for
ACK time, the A75(1) generates a PROGRESS message (➁) of [PTYPE] SMD ACK (1D)
with the flag set to ‘0’ (No ACK Received). This indicates that there is a communication fault
between the modems, or a fault with the second A75(2) modem
The example below shows the case when both modems have the SDM Auto ACK disabled. No
ACK is sent or expected.
SDM
ACK
Delay
Time
ACK
RS232 over air RS232
2
p 1D1 [SIZE] [CHECKSUM]
PC(1) A75(1)
A75(2)
or Tait Orca PC(2)
1Lead In
Delay
s FF12345678Hi [SIZE] [CHECKSUM] SEND_SDM
PROGRESS
AutoACK=0or1 Auto ACK = 1
PROGRESS
ACK triggers
PROGRESS
SDM
RS232 over air RS232
PC(1) A75(1)
A75(2)
or Tait Orca PC(2)
1Lead In
Delay
SEND_SDM
Auto ACK = 0 Auto ACK = 0
PROGRESS
s FF12345678Hi [SIZE] [CHECKSUM]