Manual-Tstep-087-Modbus.pdf

Tstep-087 - RS-485 / Modbus RTU Interface Product manual section · stepper drive with step/direction output stage 1. Quick start 1. Set the drive's address on the four address switches - all off is address 1 . 2. Se…

Tstep-087 - RS-485 / Modbus RTU Interface

Product manual section · stepper drive with step/direction output stage

1. Quick start

1. Set the drive's address on the four address switches - all off is address 1.

2. Set the baud rate on S8 - off is 19200, on is 115200.

3. Wire A and B to the bus, and the shield or common to the drive's ground reference.

4. Power the drive and read registers 0x0000-0x0003.

-> 01 03 00 00 00 04 44 09 read identity from the drive at address 1

<- 01 03 08 00 87 02 00 00 01 00 07 ...

[ 0087 ] [ 0200 ] [ 0001 ] [ 0007 ]

product firmware address capabilities

A first move, once that works:

1. 0x10 0x0204 qty 4 cruise speed and move distance

2. 0x06 0x020A value 1 move clockwise

3. 0x03 0x0300 qty 6 poll until bit 0 of the state word clears

2. Bus settings

Standard Modbus RTU over RS-485, 2-wire half duplex

Format 8 data bits, no parity, 1 stop bit (8N1)

Baud 19200 or 115200, by switch

Address 1-16, by switch

Broadcast address 0, executed but never answered

Direction control automatic, driven by the drive

Setting the address

Turning a switch on adds its weight:

Address = 1 + (8·S7 + 4·S6 + 2·S5 + 1·S4)

Addr S7 S6 S5 S4 Addr S7 S6 S5 S4

1 off off off off 9 on off off off

2 off off off on 10 on off off on

3 off off on off 11 on off on off

4 off off on on 12 on off on on

5 off on off off 13 on on off off

6 off on off on 14 on on off on

7 off on on off 15 on on on off

8 off on on on 16 on on on on

Setting the baud rate

S8 Baud

off 19200

on 115200

S9 and S10

Reserved for future use. Not read by this firmware - their position has no effect. Do not use them to configure

anything.

Switch changes are read once at power-up. Change a switch, then power-cycle the drive.

Addresses and other products

Tstep-087 drives occupy 1-16, TIO-0808 I/O cards 17-24. The ranges do not overlap.

3. Frame format and CRC

Every request and every reply follows the same layout:

[ address ][ function ][ data ... ][ CRC low ][ CRC high ]

• Frames are separated by silence, not a terminator - at least 3.5 character times of no

traffic on the line marks the end of one frame and the start of the next.

• Send a whole frame in one write call. A pause inside a frame - even a few milliseconds - is

read as end-of-frame, which splits the transmission into two fragments and fails CRC on both.

• Maximum frame length is 64 bytes. Anything longer is discarded.

CRC-16/MODBUS

The checksum is CRC-16 with polynomial 0xA001 (reflected), initial value 0xFFFF, no final XOR - the standard

Modbus CRC, not the CRC-16/CCITT or CRC-32 used by some other protocols.

It is computed over every byte from the address through the last data byte - the function code and all data, but not the

CRC bytes themselves.

The CRC is the one field sent low byte first. Every other multi-byte value on this bus - register addresses, quantities,

error in master implementations, because published CRC-16/MODBUS test vectors are usually quoted as the 16-bit

value, and it is easy to forget that the value must be byte-swapped before it goes on the wire.

Reference implementation

uint16_t crc16_modbus(const uint8_t *data, int length)

{

uint16_t crc = 0xFFFF;

for (int i = 0; i < length; i++) {

crc ^= data[i];

for (int bit = 0; bit < 8; bit++) {

if (crc & 1) crc = (crc >> 1) ^ 0xA001;

else crc = crc >> 1;

}

return crc;

}

// appending it to a frame buffer of length n (address .. last data byte)

uint16_t crc = crc16_modbus(frame, n);

frame[n] = (uint8_t)(crc & 0xFF); // low byte first

frame[n + 1] = (uint8_t)(crc >> 8);

Worked check

For the frame 01 03 00 00 00 04 (address 1, read holding registers, start 0x0000, quantity 4):

CRC value = 0x0944

on the wire, low byte first = 44 09

complete frame = 01 03 00 00 00 04 44 09

The standard CRC-16/MODBUS check value for the ASCII string "123456789" is 0x4B37 - useful for confirming a

from-scratch implementation independently of anything specific to this product.

If your framing and CRC are correct, every request frame printed in the worked examples in this manual will

reproduce byte for byte. That is the fastest way to confirm an implementation before it goes anywhere near a real

device: compute the frame, compare it to the one printed here, and only then put it on the wire.

4. Function codes

Code Name Limit

0x03 Read Holding Registers 8 registers per request

0x04 Read Input Registers identical behaviour to 0x03

0x06 Write Single Register -

0x10 Write Multiple Registers 4 registers per request

Any other function code returns exception 01.

32-bit values

Most values on this drive are 32-bit - steps, speeds and positions. Each occupies two consecutive registers, starting

on an even address, high word first:

value = (register[n] << 16) | register[n+1]

That order is fixed and not configurable. Position is signed (two's complement across the pair); everything else is

unsigned.

The 4-register write limit means one transaction carries two 32-bit values.

5. Register map

Identity - read only

0x0000 Product ID 0x0087

0x0001 Firmware version 0x0200 = version 2.00

0x0002 Unit address 1-16, as set by the switches

0x0003 Capabilities 0x0007 - bit 0 motion, bit 1 potentiometer, bit 2 IN1/IN2

Motion parameters - read/write

Registers Name Units Min Max

0x0200-0x0201 Acceleration steps/s² 1 1000000

0x0202-0x0203 Start speed steps/s 1 100000

0x0204-0x0205 Cruise speed steps/s 1 100000

0x0206-0x0207 Move distance steps 0 2147483647

0x0208-0x0209 Dwell ms - not implemented

0x020A Command - writing this executes

0x020B Command sequence - see section 8

Parameters are staged, not applied. Writing one changes nothing about the motor - they take effect when a command

is written. This is what makes a 32-bit value safe to write as two registers: a half-updated distance sits harmlessly in the

staging area until a command acts on it.