Manual-Tstep-087-Modbus.pdf - 第4页

Values are clamped, not refused. A parameter outside its range is silently brought into range at execute time. Read the register back if you need to know what was accepted. Acceleration is honoured exactly for any value …

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.

Values are clamped, not refused. A parameter outside its range is silently brought into range at execute time. Read the

Acceleration is honoured exactly for any value in range. The start speed is the speed a ramp begins and ends at -

deceleration returns to it rather than to zero.

The dwell registers do nothing. 0x0208-0x0209 accept a value, clamp it and read back correctly, but nothing acts on

it, and state word bit 0x0004 ("waiting on a dwell") can never be set. A master needing a pause between moves must

time it itself.

Live status - read only

Registers Name Units

0x0300-0x0301 Current speed steps/s

0x0302-0x0303 Position steps, signed

0x0304 State word bitmask, below

0x0305 Inputs bit 0 = IN1, bit 1 = IN2

Six contiguous registers in polling order - one 0x03 request with quantity 6 returns the drive's entire live state.

Position counts every step, in every mode - finite moves, continuous runs and seeks alike.

State word - 0x0304

Bit Meaning

0x0001 Moving

0x0002 Direction is clockwise

0x0004 Waiting on a dwell - never set, see above

0x0008 Potentiometer speed control enabled

0x0010 Driver fault - see section 7

Unmapped registers

0x0004-0x01FF, 0x020C-0x02FF and 0x0306 upward are holes and return exception 02.

6. Commands - write to 0x020A

Value Command Uses

Stop - ramps down,

never a hard stop

1 Move clockwise distance, speeds, acceleration

2 Move anticlockwise distance, speeds, acceleration

Run clockwise until

stopped

speeds, acceleration

Run anticlockwise until

stopped

speeds, acceleration

5 Seek input 1 speeds, acceleration

6 Seek input 2 speeds, acceleration

Reset position counter to

zero

Save parameters to

flash

refused while moving - see below

13 / 14

Potentiometer enable /

disable

17 / 18 Driver enable / disable

Clear a latched driver

fault

refused while the fault is live

Value Command Uses

Apply the staged cruise

speed

retargets a move already running

An unrecognised command returns exception 03 rather than being ignored.

Waiting for a move to finish

Poll 0x0300 quantity 6 and watch bit 0 of the state word. Polling every 50-100 ms is ample.

Command 8 - save parameters to flash

Stores acceleration, start speed, cruise speed and move distance to the drive's parameter page. They are reloaded at

every power-up.

Refused with exception 03 while the motor is moving. Erasing a flash page stalls the CPU for tens of milliseconds -

this save measured 42 ms against a normal 5 ms reply - and the step generator runs from that same flash. A save during

a move would starve the step interrupt and silently drop every step it should have emitted: roughly 40 at 1000 steps/s,

thousands at full speed, leaving the position counter wrong with nothing to indicate it. Stop first.

Budget 50 ms for the reply, not the usual 5 ms. A master with a tight timeout will call this a failure and may retry a save

that already succeeded.

The dwell registers are not persisted, and neither is anything else outside the four values above.

Changing speed while moving

Stage a new cruise speed in 0x0204-0x0205, then write command 20. The drive ramps to the new speed at the

configured acceleration - it is never asked for a jump it cannot follow.

Command 20 is refused while the potentiometer is enabled, because the potentiometer would overwrite the new

target within a fraction of a second.

Changing direction while moving

Sending command 3 or 4 while a continuous run is already going is a reversal: the drive winds down to its start speed,

changes direction at zero speed, and takes the motion back up. You do not have to sequence a stop yourself. Position

tracks correctly throughout.

A reversal during a finite move is refused (exception 03). Stop the move, then command the new direction.

Potentiometer

Command 13 enables it, 14 disables it. While enabled the potentiometer scales the cruise speed register, so it can

never ask for more than the axis is configured for, and it owns the speed target - use command 20 only with the

potentiometer disabled.

[!] Turning the knob to its minimum does not stop the motor. It commands 1 step/s, the motor keeps turning, and the

moving bit stays set. Only command 0 stops a move. If a machine needs the knob to mean stop, the master must

detect the speed floor and issue the stop itself.

[!] Seeks have no distance limit and no timeout

Commands 5 and 6 run until their input asserts. Nothing else stops them. If the input is not wired, not powered, or the

axis is already past it, the motor runs indefinitely.

A master issuing a seek must impose its own limit - a timeout, a travel budget, or both - and send command 0 when it

expires. Confirm that register 0x0305 actually changes before relying on a seek at all.

7. Safety and fault handling

These are properties of the drive that a master must design around.

• The bus is the only source of commands. The drive is always online; nothing else can take the

motor away from a master mid-operation.

• The drive answers while it is moving. Position reads and a stop work mid-move - this is what

makes a bus stop usable at all.

• A stop over the bus is not a safety function. It travels over a wire, through a UART, into a

polled loop. The hardwired emergency-stop chain remains what makes a machine safe.