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Modbus RTU/TCP
Here are three demos to read a value from STM32 devices using `mbpoll' in Linux.
RTU
RS232
The current temperature of an LM75 I2C sensor is read in Q8.8 format.
This demo uses the Nucleo U575ZI Cortex-M33 development board.
Two TTYs are utilised. The ST-LINK tty is used for the modbus I/O and the other for debug output and was only needed during development so can be ignored.
RS485
This demo uses the Nucleo H7A3ZI-Q Cortex-M7 development board.
The mobbus I/O with this demo uses a MAX485 transceiver and demonstrates how to utilise it.
TCP
This demo uses the Nucleo G491RE and the ENC28J60. It depends on FreeRTOS with FreeRTOS-PLUS-TCP.
VREFINT is read as an input to the STM32 internal ADC.
Install
Firmware
Install mercurial if needed then fetch stm32 microcontroller tests.
hg clone http://hg.kewl.org/pub/Archimedes
Toolchain
Refer to README in the source directory and install dependencies.
mbpoll
apt install mbpoll
STM32U575
make -f Makefile.u575zi program debug
References
| Register | Address | Format | Mode | Comment |
|---|---|---|---|---|
| LM75 temperature | 0x75 | Q8.8 | Read only | Divide by 256.0 to convert to floating point |
Peek
mbpoll parameter breakdown:
- Verbose output: -v
- Parity: -P none
- Slave address: -a 1
- Reference base zero: -0
- Poll once: -1
- Reference: -r 0x75
- 16-bit register: -t 4:hex
- 2 stop bits: -s 2
- 1 register: -c 1
mbpoll -v -P none -a 1 -0 -1 -r 0x75 -t 4:hex -s 2 -c 1 /dev/ttySTLINK3-U575
debug enabled
Set rtu parity=none
iGetIntList(1)
Integer found: 1
iCount=1
Set start reference=117
Set function=4
Set format=hex
Set rtu stop bits=2
Set number of values=1
Set mode to RTU for serial port
Set device=/dev/ttySTLINK3-U575
mbpoll 1.0-0 - FieldTalk(tm) Modbus(R) Master Simulator
Copyright © 2015-2019 Pascal JEAN, https://github.com/epsilonrt/mbpoll
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions; type 'mbpoll -w' for details.
Opening /dev/ttySTLINK3-U575 at 19200 bauds (N, 8, 2)
Set response timeout to 1 sec, 0 us
Protocol configuration: Modbus RTU
Slave configuration...: address = [1]
start reference = 117, count = 1
Communication.........: /dev/ttySTLINK3-U575, 19200-8N2
t/o 1.00 s, poll rate 1000 ms
Data type.............: 16-bit register, output (holding) register table
-- Polling slave 1...
[01][03][00][75][00][01][95][D0]
Waiting for a confirmation...
<01><03><02><1A><00><B3><24>
[117]: 0x1A00
The response above is the Q8.8 value of the temperature where 0x1A00 represents 26 degrees Celcius.
If an error occurs reading the temperature, the value returned would be -1 (0xFFFF) which is an invalid value and cannot be achieved in normal use.
STM32G491
peek
mbpoll -v -a 1 -0 -1 -r 0x100 -t 4 -c 1 192.168.0.205
debug enabled
iGetIntList(1)
Integer found: 1
iCount=1
Set start reference=256
Set function=4
Set number of values=1
Set device=192.168.0.205
mbpoll 1.0-0 - FieldTalk(tm) Modbus(R) Master Simulator
Copyright © 2015-2019 Pascal JEAN, https://github.com/epsilonrt/mbpoll
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions; type 'mbpoll -w' for details.
Connecting to [192.168.0.205]:502
Set response timeout to 1 sec, 0 us
Protocol configuration: Modbus TCP
Slave configuration...: address = [1]
start reference = 256, count = 1
Communication.........: 192.168.0.205, port 502, t/o 1.00 s, poll rate 1000 ms
Data type.............: 16-bit register, output (holding) register table
-- Polling slave 1...
[00][01][00][00][00][06][01][03][01][00][00][01]
Waiting for a confirmation...
<00><01><00><00><00><05><01><03><02><0C><CB>
[256]: 3275
tcpdump
tcpdump host stm32g4 and port 502 -X
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on wlan0, link-type EN10MB (Ethernet), snapshot length 262144 bytes
12:06:19.553003 IP pi1.kewl.org.58674 > stm32g4.kewl.org.502: Flags [S], seq 1040100054, win 64240, options [mss 1460,sackOK,TS val 3692783361 ecr 0,nop,wscale 7], length 0
0x0000: 4510 003c 521f 4000 4006 65ce c0a8 00a1 E..<R.@.@.e.....
0x0010: c0a8 00cd e532 01f6 3dfe aad6 0000 0000 .....2..=.......
0x0020: a002 faf0 b735 0000 0204 05b4 0402 080a .....5..........
0x0030: dc1b 6701 0000 0000 0103 0307 ..g.........
12:06:19.558698 IP stm32g4.kewl.org.502 > pi1.kewl.org.58674: Flags [S.], seq 1354047842, ack 1040100055, win 536, options [mss 536], length 0
0x0000: 4510 002c 0014 0000 8006 b7e9 c0a8 00cd E..,............
0x0010: c0a8 00a1 01f6 e532 50b5 2162 3dfe aad7 .......2P.!b=...
0x0020: 6012 0218 d4c5 0000 0204 0218 0000 `.............
12:06:19.558806 IP pi1.kewl.org.58674 > stm32g4.kewl.org.502: Flags [.], ack 1, win 64240, length 0
0x0000: 4510 0028 5220 4000 4006 65e1 c0a8 00a1 E..(R.@.@.e.....
0x0010: c0a8 00cd e532 01f6 3dfe aad7 50b5 2163 .....2..=...P.!c
0x0020: 5010 faf0 f00d 0000 P.......
12:06:19.579324 IP pi1.kewl.org.58674 > stm32g4.kewl.org.502: Flags [P.], seq 1:13, ack 1, win 64240, length 12
0x0000: 4510 0034 5221 4000 4006 65d4 c0a8 00a1 E..4R!@.@.e.....
0x0010: c0a8 00cd e532 01f6 3dfe aad7 50b5 2163 .....2..=...P.!c
0x0020: 5018 faf0 edee 0000 0001 0000 0006 0103 P...............
0x0030: 0100 0001 ....
12:06:19.580447 IP stm32g4.kewl.org.502 > pi1.kewl.org.58674: Flags [.], ack 13, win 536, length 0
0x0000: 4510 0028 0015 0000 8006 b7ec c0a8 00cd E..(............
0x0010: c0a8 00a1 01f6 e532 50b5 2163 3dfe aae3 .......2P.!c=...
0x0020: 5010 0218 e8da 0000 0000 0000 0000 P.............
12:06:19.581469 IP stm32g4.kewl.org.502 > pi1.kewl.org.58674: Flags [P.], seq 1:12, ack 13, win 536, length 11
0x0000: 4510 0033 0016 0000 8006 b7e0 c0a8 00cd E..3............
0x0010: c0a8 00a1 01f6 e532 50b5 2163 3dfe aae3 .......2P.!c=...
0x0020: 5018 0218 1ab2 0000 0001 0000 0005 0103 P...............
0x0030: 020c cb ...
12:06:19.581605 IP pi1.kewl.org.58674 > stm32g4.kewl.org.502: Flags [.], ack 12, win 64229, length 0
0x0000: 4510 0028 5222 4000 4006 65df c0a8 00a1 E..(R"@.@.e.....
0x0010: c0a8 00cd e532 01f6 3dfe aae3 50b5 216e .....2..=...P.!n
0x0020: 5010 fae5 f001 0000 P.......
12:06:19.581868 IP pi1.kewl.org.58674 > stm32g4.kewl.org.502: Flags [F.], seq 13, ack 12, win 64229, length 0
0x0000: 4510 0028 5223 4000 4006 65de c0a8 00a1 E..(R#@.@.e.....
0x0010: c0a8 00cd e532 01f6 3dfe aae3 50b5 216e .....2..=...P.!n
0x0020: 5011 fae5 f000 0000 P.......
12:06:19.582625 IP stm32g4.kewl.org.502 > pi1.kewl.org.58674: Flags [R.], seq 12, ack 13, win 64229, length 0
0x0000: 4510 0028 0017 0000 8006 b7ea c0a8 00cd E..(............
0x0010: c0a8 00a1 01f6 e532 50b5 216e 3dfe aae3 .......2P.!n=...
0x0020: 5014 fae5 effd 0000 0000 0000 0000 P.............
12:06:19.582921 IP stm32g4.kewl.org.502 > pi1.kewl.org.58674: Flags [R.], seq 12, ack 13, win 64229, length 0
0x0000: 4510 0028 0018 0000 8006 b7e9 c0a8 00cd E..(............
0x0010: c0a8 00a1 01f6 e532 50b5 216e 3dfe aae3 .......2P.!n=...
0x0020: 5014 fae5 effd 0000 0000 0000 0000 P.............
