// AutomationDirect DURApulse GS20 / GS20X

DURApulse GS20
Modbus registers

The GS20 spares you the lookup table: every parameter address follows from the parameter number with one small calculation, and two fixed registers run the drive. This page gives the formula, the two control words, and a bench procedure that confirms both against the keypad before a PLC is anywhere near the panel.

Download Pro trial — free 14 days Jump to the verification steps

Windows 10/11 · RS-485 adapter · No PLC needed to test

// the formula worth knowing

Any GS20 parameter becomes a register with one calculation

Most drive documentation makes you hunt through a table to find the Modbus address of a parameter. The DURApulse GS20 does not need one: the address follows directly from the parameter number, and the manual shows the arithmetic.

Take the group number as the high byte and the parameter number as the low byte, both in hex. Acceleration time 1 is P01.12: group 01 gives 0100, parameter 12 is 0x0C, and the register is 0x010C — 268 in decimal.

Once you have that, every parameter in the drive is reachable without a lookup table, which also means a mistyped group number lands you on a completely unrelated parameter. Reading before writing is not optional here.

The conversion

register = (group × 0x100) + parameter, both in hex. P01.12 → 0x0100 + 0x0C = 0x010C = 268 decimal.

Also on this site
// control words

Two registers run the drive

These are documented in the GS20 user manual’s serial communications chapter. They sit outside the parameter space, at addresses that will look familiar to anyone who has worked with Delta-based drives.

What it isHexDecimalPurpose
Control Word 10x20008192Run, stop and related commands
Control Word 20x20018193Commanded frequency
A useful coincidence: 0x2000 and 0x2001 are the same addresses used for the command and reference words on Allen-Bradley PowerFlex drives. If a panel mixes the two families, the addresses look identical while the bit meanings and scaling do not — which is a good reason to read each drive’s status word and watch it change before writing anything.

The drive also offers block transfer registers, configured through the P09 group, which let a master collect scattered parameters in a single request instead of six. On a slow serial line with several drives that difference is worth having. Protocol selection between Modbus RTU and ASCII is made in P09.04.

// bench test before the plc

Four reads and one write

Because the parameter addresses come from a formula, the fastest way to build confidence is to read a parameter whose value you can see on the keypad, and confirm the two match.

1
Step 1
Set the protocol and serial settings
Choose Modbus RTU or ASCII in P09.04 and set the address and baud rate in the same group. Only one serial protocol runs at a time. If your PLC has RS-232 only, an RS-485 converter sits between them — the drive itself expects RS-485.
2
Step 2
Read a parameter you can see
Pick a parameter whose value is visible on the keypad, convert its number with the formula and read that register. The keypad and the register must agree. This single check validates the formula, the address, the baud rate and the wiring in one go.
3
Step 3
Read the running frequency
Poll the output frequency continuously and change the setpoint from the keypad. A value that tracks the display proves you are reading live data rather than a stale or unrelated register.
4
Step 4
Write the frequency command
Write to Control Word 2 at 0x2001, then read the actual output frequency and calculate the scaling from what the drive did. Two different written values give you the factor with no ambiguity, which is safer than trusting a figure from a forum.
5
Step 5
Command run and stop last
Write Control Word 1 at 0x2000 only when the drive is in a safe state and the motor is uncoupled or free to turn. By this point the status is readable and the reference is proven, so anything that goes wrong has a short list of causes.
ModbusManager reads and writes both control words from the same window, shows every value in decimal, hex and binary, and logs each request and response — so the formula can be checked against the keypad in seconds. For a line of several GS20 drives, the gateway function merges the registers you choose into one common map that a PLC reads with a single connection.
// frequently asked questions

FAQ

How do I find the Modbus address of a GS20 parameter?+
Use the group number as the high byte and the parameter number as the low byte, in hex. Acceleration time 1 is P01.12, so group 01 gives 0100, parameter 12 is 0x0C, and the register is 0x010C, which is 268 in decimal. Every parameter follows the same rule, so no lookup table is needed.
Where are the run command and frequency command?+
Control Word 1 at 0x2000, which is 8192 decimal, carries run, stop and related commands. Control Word 2 at 0x2001, which is 8193 decimal, carries the commanded frequency. Both sit outside the parameter address space.
Does the GS20 speak Modbus RTU or ASCII?+
Both, but only one at a time. The protocol is selected in parameter P09.04, along with the address and baud rate in the same group. If a serial Modbus link and an Ethernet option card are both fitted, they can run simultaneously.
What are the block transfer registers for?+
They let you gather parameters that are scattered across the address map into a contiguous block, so a master can collect them in one request instead of several. On a slow serial line shared by multiple drives, that turns six messages into one.
The addresses look the same as an Allen-Bradley drive. Are they interchangeable?+
The addresses coincide, but nothing else does. Bit meanings, scaling and the conditions under which a drive accepts a command all differ between families. In a panel that mixes them, read each drive's status word and watch it change before writing anything.
Can I test this without a PLC?+
Yes, and it is the faster route. A Windows Modbus master on an RS-485 adapter reads a parameter you can see on the keypad, which validates the formula and the link at once. Only after that do the numbers go into PLC code.

Check the formula against your own drive

Read a parameter, compare it with the keypad, then write the control words — from a laptop, before the PLC program exists. Free for 14 days.

Download Pro trial Or the Standard edition

Windows 10/11 · Modbus RTU, ASCII and TCP · One-time license