RxPDO not working - slave.input is read-only, slave.output has zero length

[maihongda1989]

Title: RxPDO not working for Digital Output modules - slave.input is read-only, slave.output has zero length

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Environment

• PySOEM Version: 1.1.12
• Python: 3.12.7
• OS: Windows 10/11
• Device: Leadshine EM32DO-E4 (32-bit Digital Output Module)

Problem

Cannot write to digital output modules via PDO. The device has proper RxPDO mapping in ESI, but:

1. slave.input - 4 bytes but read-only (no setter)
2. slave.output - 0 bytes (not allocated)

do_slave = master.slaves[1]  # EM32DO-E4

# After config_map()
print(len(do_slave.input))   # 4 bytes
print(len(do_slave.output))  # 0 bytes ❌

# Try to write
do_slave.input = b'\xFF\xFF\xFF\xFF'
# AttributeError: property 'input' of 'CdefSlave' object has no setter ❌

Expected Behavior

Based on your basic_example.py (Beckhoff EL1259):

self._master.slaves[2].output = bytes(tmp)  # Should work

Device Configuration

ESI file has correct RxPDO:

<RxPdo Mandatory="true" Fixed="true" Sm="2">
    <Index>#x1600</Index>
    <Entry>
        <Index>#x7000</Index>
        <SubIndex>1</SubIndex>
        <BitLen>16</BitLen>
    </Entry>
    <Entry>
        <Index>#x7000</Index>
        <SubIndex>2</SubIndex>
        <BitLen>16</BitLen>
    </Entry>
</RxPdo>

<Sm StartAddress="#x1800" ControlByte="#x64" Enable="1">Outputs</Sm>

Current Workaround

Only SDO works (non-realtime, ~10Hz):

do_slave.sdo_write(0x7000, 1, struct.pack('<I', value))

Diagnostic Output

=== Slave 1: EM32DO-E4 ===
input buffer (RxPDO: Master→Slave):
   Type:   bytes
   Length: 4 bytes
   Content: 00000000
   Writability test:
      [FAIL] slave.input cannot be assigned: property 'input' of 'CdefSlave' object has no setter

output buffer (TxPDO: Slave→Master):
   Type:   bytes
   Length: 0 bytes
   Writability test:
      - Length is 0, cannot test

Available methods:
   - _get_input
   - _get_output
   - _set_output
   - input
   - output

Comparison

DI Module (EM32DI-E4) - Works perfectly:

input buffer: 0 bytes
output buffer: 4 bytes ✓
slave.output = b'...'  # Works! ✓

Questions

1. Why is slave.output not allocated for devices with RxPDO?
2. Should slave.input have a setter for RxPDO devices?
3. Is there a _set_output() or similar method we should use?

Suggested Fix

One of:

1. Add setter for slave.input property
2. Allocate slave.output buffer for RxPDO devices
3. Provide write_output_pdo(data) method
4. Document the correct approach if we're doing it wrong

Full Diagnostic Script

Can provide complete test script and ESI files if needed.

This blocks real-time digital output control for many industrial devices.

Thank you for this great library!

[bnjmnp]

Hi, Yes, could you please provide a complete script, ideally also the ESI file? There might be something missing in your script regarding the PDO selection object 0x1C12.

[addingding]

same to #183