ST METERS AND MORE UM2241 User manual

August 2017
DocID030767 Rev 1
1/26
www.st.com
UM2241
User manual
METERS AND MORE®compliant power line communication
system-on-chip
Introduction
This user manual, which targets application developers, provides complete information on how to use
the ST75MM in applications by describing the host interface, the available protocol services and the MIB
accessible through the host interface. For ordering information, mechanical and electrical device
characteristics, please refer to the ST75MM datasheet available at www.st.com.

Contents
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Contents
1Host interface ..................................................................................6
1.1 Settings.............................................................................................6
1.2 Operations.........................................................................................6
1.3 Acknowledge.....................................................................................7
1.4 Command frame format ....................................................................7
1.5 Status message frame format (SM) ..................................................7
1.6 TREQ management..........................................................................9
1.7 Examples ..........................................................................................9
2Host interface commands.............................................................14
2.1 Commands......................................................................................14
2.2 Error codes......................................................................................14
2.3 MIB_Write .......................................................................................15
2.3.1 MIB_Write request............................................................................ 15
2.3.2 MIB_Write positive confirm............................................................... 15
2.3.3 MIB_Write negative confirm ............................................................. 15
2.3.4 MIB_Write indication......................................................................... 15
2.4 MIB_Read.......................................................................................15
2.4.1 MIB_Read request............................................................................ 16
2.4.2 MIB_Read positive confirm .............................................................. 16
2.4.3 MIB_Read negative confirm............................................................. 16
2.5 BIO_Reset.......................................................................................16
2.5.1 BIO_Reset request........................................................................... 16
2.5.2 BIO_Reset positive confirm.............................................................. 16
2.5.3 BIO_Reset negative confirm ............................................................ 17
2.5.4 BIO_Reset indication........................................................................ 17
2.6 DL_DATA_SLAVE ..........................................................................17
2.6.1 DL_DATA_SLAVE indication ........................................................... 17
2.7 HI_Ping ...........................................................................................18
2.7.1 HI_PING request .............................................................................. 18
2.7.2 HI_PING positive confirm................................................................. 18
2.8 HI_Error ..........................................................................................18
2.8.1 HI_ERROR indication....................................................................... 18
3Management information base (MIB)...........................................19
3.1 MIB objects .....................................................................................19

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4Configuring the ST75MM ..............................................................23
4.1 PHY configuration (MIB index 2).....................................................23
4.2 MAC configuration (MIB index 3) ....................................................24
4.3 Manufacturer data (MIB index 6).....................................................24
4.4 Custom frequencies (MIB index 23)................................................24
5Revision history ............................................................................25

List of tables
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List of tables
Table 1: Command frame format................................................................................................................7
Table 2: Status message format.................................................................................................................7
Table 3: Modem status format....................................................................................................................8
Table 4: MIB status format..........................................................................................................................8
Table 5: Available commands...................................................................................................................14
Table 6: List of error codes.......................................................................................................................14
Table 7: Reset cause byte format.............................................................................................................17
Table 8: MIB objects list............................................................................................................................19
Table 9: MAC data MIB object (1) ............................................................................................................19
Table 10: PHY configuration MIB object (2) .............................................................................................19
Table 11: MAC configuration MIB object (3).............................................................................................20
Table 12: Manufacturer data MIB object (6).............................................................................................21
Table 13: Host interface timings MIB object (14)......................................................................................21
Table 14: ZC alarm MIB object (18)..........................................................................................................21
Table 15: PHY custom frequencies MIB object (23).................................................................................21
Table 16: PHY statistics MIB object (24) ..................................................................................................21
Table 17: PHY configuration values for CENELEC 132.5 kHz operations...............................................23
Table 18: MAC configuration values for CENELEC 132.5 kHz operations ..............................................24
Table 19: Document revision history ........................................................................................................25

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List of figures
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List of figures
Figure 1: Host controller to ST75MM connection scheme..........................................................................6
Figure 2: TREQ negotiation timing diagram ...............................................................................................9
Figure 3: DL_DATA_SLAVE.indication transaction..................................................................................10
Figure 4: DL_DATA_SLAVE.indication transaction in case of no ack......................................................11
Figure 5: MIB_Write.request transaction..................................................................................................12
Figure 6: MIB_Read.request transaction..................................................................................................13

Host interface
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1 Host interface
1.1 Settings
The host interface is used to interface the ST75MM to the host controller, it allows
exchanging data, configuration and control messages.
The host interface can be managed by the host controller with a half-duplex asynchronous
serial port (UART) plus an additional synchronization signal which will be referenced, in this
document as TREQ.
The configuration at the host controller shall be the following one:
2-wire UART port set to (57600, 1, N, 1) no flow control
Single wire push-pull output (TREQ line)
Figure 1: Host controller to ST75MM connection scheme
1.2 Operations
Being the communication link between the host controller and the ST75MM a half-duplex
serial link, the communication paradigm is master/slave, where the ST75MM acts as the
master of the communication.
When an event is triggered inside the ST75MM (incoming PLC frame, completion of
requested activities or error/warning events), this is automatically and immediately sent to
the host controller through the serial link. This means that the host controller should
continuously monitor the UART port, decode the frames as they are detected and send an
acknowledge message to the ST75MM.
When the host controller needs to send a command to the ST75MM (data request or MIB
programming/reading) it shall drive low the TREQ signal (which indeed needs to remain
high when idle) and wait for the ST75MM to send a special message, the so called "Status
Message" (SM). As the SM holds information about the availability of the ST75MM to
receive commands, it shall be detected by the host controller before sending the message
request to the ST75MM. The ST75MM will respond immediately to the host controller with
an acknowledge byte and, if the command requires a further communication (e.g., the
result of the command) will be sent as an internally triggered event (see previous
paragraph) once the operations inside the ST75MM are concluded.

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Section 1.7: "Examples" contains some examples on how complex operations shall be
managed between the host controller and the ST75MM.
1.3 Acknowledge
In order to improve the serial link robustness, every frame except the SM must be
acknowledged by the receiver within a given period TACK (host interface timings are
managed through a dedicated MIB object, see Section 3.1: "MIB objects" for reference),
otherwise the sender will repeat once the same message waiting for a new acknowledge. If
no acknowledge arrives after the second message is sent, the message is discarded by the
sender and no further repetitions are sent. If the sender is the ST75MM, no further action is
taken.
The acknowledge byte is only linked to the format of the frame, and shall never give
feedback on the validity or execution of the command; it can have two values:
0x06 (ACK) which means that the received command is well formed
0x15 (NAK) which means that the received command has errors (length or CRC).
1.4 Command frame format
Commands are formatted as follows:
Table 1: Command frame format
Starting
Byte
Field
Size
Value
Description
0
Frame
start
1
0x02 /
0x03
Used to mark the start of a command. In order for the
host controller to distinguish between a message and its
repetition(1). The frame start has always the value 0x02,
except for repeated messages, where a value of 0x03 is
used. When the host controller receives a message
starting with 0x03 it should verify if the same message
has already been received, and, in this case, discards
the latter one.
1
Length
1
Any
Number of payload bytes after the first one (always
sent).
2
Command
code
1
Any
Identifies the command to be executed.
3
Payload
1...256
Any
Contains the parameters associated with the command.
Length +
4
Checksum
2
Any
Sum of the Length, Command code and Payload fields.
The sum is performed byte-wise, represented as 16-bit
value and sent to the host controller MSB first.
Notes:
(1)This condition is generated when the modem doesn’t receive the ACK message from the host controller within
the proper TACK time.
1.5 Status message frame format (SM)
The SM is formatted as follows:
Table 2: Status message format
Starting
Byte
Field
Size
Value
Description

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Starting
Byte
Field
Size
Value
Description
0
SM start
1
0x3F
Used to mark the start of the SM
1
Modem
status
1
Any
Bit mask showing the status of the ST75MM modem
2
MIB status
2
Any
Bit mask showing which MIB objects have been
reconfigured by the host controller
The following table shows the modem status field possible values.
Table 3: Modem status format
Bit
Sub-field
Values
Description
0
SET
0
1
The ST75MM modem has an internal configuration error.
The ST75MM modem is configured and running properly.
1
TX
0
1
The ST75MM is not transmitting.
The ST75MM is transmitting.
2
RX
0
1
The ST75MM is not in active reception state.
The ST75MM is receiving a PLC frame.
3
PLC busy(1)
0
1
PHY layer is in idle state.
PHY layer is busy or not yet configured.
4
OVC
0
1
No overcurrent events registered during the last transmission.
At least one overcurrent event registered during the last transmission.
5
Reserved
-
-
6-7
Temperature
00(2)
01
10
11
ST75MM temperature is lower than 70 °C.
ST75MM temperature is between 70 °C and 100 °C.
ST75MM temperature is between 101 °C and 125 °C.
ST75MM temperature is higher than 125 °C.
Notes:
(1)Before sending any command to the ST75MM the host controller should monitor this flag, proceeding only if the
value is 0.
(2)Values are always given as [msb]...[lsb], so a value of “01” means bit_7 = 0 and bit_6 = 1.
The following table shows the correspondence between the MIB status field and the MIB
configuration, if the MIB has been configured (or correctly reconfigured after a reset event)
the corresponding bit is raised, otherwise is set to 0.
Table 4: MIB status format
Bit
Name
MIB index
Description
0
Reserved
-
-
1
Reserved
-
-
2
PHY configuration
2
Current PHY layer configuration
3
MAC configuration
3
Current MAC layer configuration
4
Reserved
-
-
5
Reserved
-
-

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Bit
Name
MIB index
Description
6
Manufacturer data
6
Physical address (ACA) of the modem and serial number
7
Reserved
-
-
8
Reserved
-
-
9
Reserved
-
-
10
Reserved
-
-
11
Reserved
-
-
12
Reserved
-
-
13
Reserved
-
-
14
Reserved
-
-
15
Reserved
-
-
1.6 TREQ management
Here below a timing diagram of the priority negotiation of the serial link is depicted, first of
all the host controller wanting to send a command to the ST75MM drives low the TREQ
line, waiting for the SM frame before sending the message.
As soon as the SM frame starts, the host controller drives high the TREQ line and, when
the SM is completely received, it verifies that PLC Busy flag is disabled.
If the PLC Busy flag of the SM is disabled the host controller sends the command to the
ST75MM within TSR time, and waits for a maximum of TACK time the acknowledge byte from
the ST75MM.
If the acknowledge byte is not received within TACK time, the host controller can initiate a
new transaction, sending the same command with 0x03 as start of the frame byte, this way,
if the acknowledge byte has been lost in the serial link the ST75MM receives the command
twice and can disregard the repetition.
Figure 2: TREQ negotiation timing diagram
1.7 Examples
Here below an example of DL_DATA_SLAVE.indication coming from the ST75MM, in this
case, as in MIB_Write.indication, being the message triggered by the ST75MM there is no
negotiation with the host controller in the serial link.

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Figure 3: DL_DATA_SLAVE.indication transaction
The same transaction, in case the acknowledge (the same applies in case the –indication
is lost) is lost, is the one depicted in the next figure, where the second
DL_DATA_SLAVE.indication message frame uses 0x03 as start of the frame byte instead
0x02 as the first one, to let the host controller check if the message has already been
received or not.
.

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Figure 4: DL_DATA_SLAVE.indication transaction in case of no ack
This is an example of the MIB_Write request coming from the host controller, as the
initiator is the host controller, the session is started with the negotiation with the ST75MM
to gain priority on the serial link

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Figure 5: MIB_Write.request transaction
The MIB_Read request coming from the host controller follows the same mechanism as
the MIB_Write.

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Figure 6: MIB_Read.request transaction

Host interface commands
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2 Host interface commands
2.1 Commands
The following table is a summary of the available commands, each command will be better
specified later on.
Table 5: Available commands
Command
.request
.confirm
(positive)
.indication
.confirm
(negative)
Description
MIB_Write
0x08
0x09
0x0A
0x0B
Modifies the value of a
specific MIB object
(.request) or notifies
about an internally
triggered modification
(.indication).
MIB_Read
0x0C
0x0D
-
0x0F
Reads the current value
of a specific MIB object.
DL_DATA_SLAVE
-
-
0x26
-
Notifies about data
packet received over the
power line.
HI_Ping
0x2C
0x2D
-
-
Host interface loop, used
to monitor the healthy
state of the serial link
and modem.
HI_Error
-
-
-
0x36
Notifies about the
reception of an unknown
command.
BIO_Reset
0x3C
0x3D
0x3E
0x3F
Triggers a SW reset
(.request) or notifies
about an internally
triggered reset event
(.indication).
2.2 Error codes
Table 6: List of error codes
Value
Error
Description
0x02
WPL
Wrong argument or parameter length
0x03
WPV
Wrong argument or parameter value
0x04
BUSY
Subsystem which is supposed to perform the operation is busy
0x06
NOT_PRESENT
Subsystem which is supposed to perform the operation is either not
present or not connected
0x07
DISABLED
Subsystem which is supposed to perform the operation is disabled
0x08
TIMEOUT
The operation has not been performed in the proper time
0xFF
ERROR
Generic error

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2.3 MIB_Write
This command is initiated by the host controller to request a modification on a specific MIB
object, the MIB object index and the expected new value are embedded in the payload of
the .request message, while the .confirm messages carry the information about the
success of the operation. The indication message is issued by the ST75MM modem when
some specific MIB objects change their values due to the internal state and events or
following a request coming from the PLC.
2.3.1 MIB_Write request
Issued by: host controller
Command code: 0x08
Payload size: variable
Payload content:
MIB object index (1 byte)
MIB content (variable)
2.3.2 MIB_Write positive confirm
Issued by: ST75MM
Command code: 0x09
Payload size: 1 byte
Payload content:
MIB object index (1 byte)
2.3.3 MIB_Write negative confirm
Issued by: ST75MM
Command code: 0x0B
Payload size: 1 byte
Payload content:
Error code (1 byte)
2.3.4 MIB_Write indication
Issued by: ST75MM
Command code: 0x0A
Payload size: variable
Payload content:
MIB object index (1 byte)
MIB value (variable)
2.4 MIB_Read
This command is initiated by the host controller to request the current value of a specific
MIB object, the MIB object index is specified in the payload of the .request message, while
the .confirm messages hold the MIB object index and its current value.

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2.4.1 MIB_Read request
Issued by: host controller
Command code: 0x0C
Payload size: 1 byte
Payload content:
MIB object index (1 byte)
2.4.2 MIB_Read positive confirm
Issued by: ST75MM
Command code: 0x0D
Payload size: variable
Payload content:
MIB current value (variable)
2.4.3 MIB_Read negative confirm
Issued by: ST75MM
Command code: 0x0F
Payload size: 1 byte
Payload content:
Error code (1 byte)
2.5 BIO_Reset
These commands are exchanged when the host controller needs to force a SW reset to the
ST75MM modem (request), at the power-on, after a hardware reset or when the ST75MM
modem reaches an instability state and internally triggers a SW reset (indication).
2.5.1 BIO_Reset request
Issued by: host controller
Command code: 0x3C
Payload size: 1 byte
Payload content:
Reserved (1 byte) –set to 0
2.5.2 BIO_Reset positive confirm
Issued by: ST75MM
Command code: 0x3D
Payload size: 1 byte
Payload content:
Reserved (1 byte)

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2.5.3 BIO_Reset negative confirm
Issued by: ST75MM
Command code: 0x3F
Payload size: 1 byte
Payload content:
Error code (1 byte)
2.5.4 BIO_Reset indication
Issued by: ST75MM
Command code: 0x3E
Payload size: 1 byte
Payload content:
Reset cause (1 byte)
Table 7: Reset cause byte format
Bit
Field
Value
Description
0-
6
Reset cause
0
1
2
3
4
5
6
7
8 -
127
Power-on or HW reset
Watchdog
SW reset
BIO_Reset request
PHY error (diagnostic)
Timer or zero crossing (diagnostic)
Inconsistent state (diagnostic)
PHY layer error (diagnostic)
Reserved
7
Reconfiguration
status
0
1
One or more reconfigurable MIB objects have not been
properly reconfigured after reset.
All the reconfigurable MIB objects have been correctly
reconfigured after reset.
2.6 DL_DATA_SLAVE
The DL_DATA_SLAVE commands provide data communication as a slave node (e.g. the
meter in meter to concentrator communication or the customer device in meter to home
communication).
2.6.1 DL_DATA_SLAVE indication
Issued by: ST75MM
Command code: 0x26
Payload size: variable
Payload content:
Protocol type (1 byte)
Request ID (1 byte)

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Applicative payload (variable)
Only commands having the protocol type equal to 0 shall be processed, if a command with
a different protocol type is received it shall be discarded and no action performed.
2.7 HI_Ping
HI_Ping commands can be used to periodically test the serial link between the host
controller and the ST75MM modem, and the healthy state of the modem itself. If the
HI_Ping fails (once or several times) a hardware reset shall be issued to restore the
ST75MM functionalities.
2.7.1 HI_PING request
Issued by: host controller
Command code: 0x2C
Payload size: variable
Payload content:
Test sequence (variable)
The test sequence can be any possible sequence and length (between 1 and 256).
2.7.2 HI_PING positive confirm
Issued by: ST75MM
Command code: 0x2D
Payload size: variable
Payload content:
Test sequence (variable)
The test sequence is the same received within the request command.
2.8 HI_Error
This command is issued by the ST75MM when a well formed command frame is received
but the command code has not been recognized.
2.8.1 HI_ERROR indication
Issued by: ST75MM
Command code: 0x36
Payload size: 1 byte
Payload content:
Command code received (1 byte)

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3 Management information base (MIB)
3.1 MIB objects
The following table shows the MIB objects present in the ST75MM modem, reserved MIB
objects should not be modified and notifications involving those MIB objects can be
ignored.
Table 8: MIB objects list
Index(1)
Name
Size
Rights(2)
Description
1
MAC data
12
RW
Statistical information related to MAC layer
2
PHY configuration
6
RWCS
PHY layer configuration
3
MAC configuration
2
RWCS
MAC layer configuration
6
Manufacturer data
22
RWCS
Node identification parameters
14
HI timings
3
RW
Host interface (UART) timings
18
ZC alarm
1
RWI
No zero crossing detected on mains alarm
23
PHY custom frequency
17
RWC
Custom frequency setting
24
PHY statistics
9
RW
PHY layer statistics
Notes:
(1)Objects not listed here with index in the range (0, 34) are reserved objects, the host controller should avoid to
change their values and disregard any MIB_Write indication related to them.
(2)R = read, W = write, C = self-reconfigured at startup, S = affect MIB state in SM, I = can generate spontaneous
MIB_Write.indication
Table 9: MAC data MIB object (1)
Byte
Field
Bit
Sub-field
Description and values
0-1
RX
stats
-
Refused UW
Counter of incoming packets rejected as MAC was
busy
2-3
-
Bad CRC
Counter of incoming packets discarded for wrong
CRC
4-5
-
Rx packet
Counter of packets received by MAC
6-7
TX stats
-
Refused packets
Not relevant
8-9
-
Requested
packets
Not relevant
10-
11
-
Timeouts
Not relevant
Table 10: PHY configuration MIB object (2)
Byte
Field
Bit
Sub-field
Description and values
0
General
settings
0
Current control
0: current control disabled
1: current control enabled

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Byte
Field
Bit
Sub-field
Description and values
1
Zero crossing
0: next transmitted frame will start immediately
1: next transmitted frame will start at the next zero
crossing event
2
RX channel
0: single channel operations
1: dual channel operations
3
TX channel
0: transmit on high channel
1: transmit on low channel
4-
5
Frequency pair
0, 1, 2: reserved
3: custom frequency (see MIB 23 for channel
frequencies)
6
BU enable
0: band in use, detector not enabled
1: band in use, detector enabled
7
CSMA enable
0: CSMA not enabled
1: CSMA enabled
1
0-
4
TX gain
Gain, in dB, applied in transmission
5-
7
TX modulation
Modulation used in transmission:
0 to 3: reserved
4: BPSK coded
5: QPSK coded
6 to 7: reserved
2
0-
1
PSK preamble
0:16 bits preamble
1: 24 bits preamble
2: 32 bits preamble
3: 40 bits preamble
2
RX low
channel
Receiving mode for lower channel
0: FSK modulation
1: any PSK modulation
3
RX high
channel
Receiving mode for higher channel
0: FSK modulation
1: any PSK modulation
4-
7
Reserved
-
3-5
Reserved
-
Reserved
-
Table 11: MAC configuration MIB object (3)
Byte
Field
Bit
Sub-field
Description and values
0
RX mode
-
-
0: RX disable
1: RX normal
2 to 255: reserved
1
TX mode
-
-
0: TX disable
1: TX normal
2 to 255: reserved