Using servos and controlling unused IO pins
RepRapFirmware allows you to connect other devices to outputs that are not required for their primary purpose. The DueX2 and DueX5 expansion boards for the Duet WiFi and Duet Ethernet also provide additional outputs.
Contents
Introduction ¶
The Gcodes M42 Switch I/O pin and M280 set servo position allow direct control of some pins, or re-purposing of those pins to control PWM hobby servos
Important note on connecting servos ¶
When a servo stops moving, it can pump a large amount of energy into the +5v rail due to regenerative braking. If unchecked, this may increase the voltage of the +5V rail above the safe limit. The 1.04 revision of the Duet WiFi/Ethernet has an extra 220uF capacitor on the 5v rail to help absorb this, so does the Duet Maestro. Older Duets don't. So when using servos with them it is advisable to add your own 220uF capacitor between the +5V and ground servo wires.
Logical pin numbers ¶
Starting with firmware version 1.16, pin numbers in the M42 command are logical pin numbers as listed below, not Arduino-like pin numbers. The M280 servo control command uses a subset of the same pin numbers.
Note that these logical pin numbers are not the physical pin numbers on the expansion header, or the internal pin numbering within the firmware.
To see where these pins are on the 2nd Generation Duets, see the Duet wiring diagrams
| Pin numbers | Usual function | PWM capable? | Usable for servos? | Notes |
|---|---|---|---|---|
| 0-7 | Heaters 0-7 | yes | yes | Disable the heater using M307 H# A-1 C-1 D-1 to make the pin available, where # is the heater number, and make sure that no tool is configured to use that heater. The outputs on the expansion connector are active low with 3.3V signal level. On the DueX5 expansion board, heater channels 3-7 are available as 5V active-high signals on the PWM1 - PWM5 connectors respectively. On the DueX2 from version 0.8a onwards, heater channels 3-7 are available on PWM1 - PWM5, prior to that heater channels 3-5 only are available on PWM1 - PWM3 . Caution: the heater output terminals will also be driven by the PWM signal or servo pulses. |
| 20-27 | Fans 0-7 | yes | 20-22 only | Disable the fan using M106 P# I-1 to make the pin available, where # is the fan number. Fans 3-7 are on the DueX5 and DueX2 expansion boards. |
| 40-49 | Endstop connectors 0-9 | no | no | 40-44 are input-only. On the Duet WiFi and Duet Ethernet, if a DueX2 or DueX5 expansion board is connected then 45-49 are the endstop connectors on the expansion board and are input-only; else they are additional endstop connections in the expansion connector. On the Duet 0.6 and 0.8.5, 45-48 are the endstop inputs on the expansion connector. |
| 60- | Miscellaneous pins | varies | varies | The pins available depend on which Duet you have - see below |
| 100- | Pins on expansion devices | varies | varies | The pins available depend on which Duet you have - see below |
Board dependencies ¶
Duet WiFi and Duet Ethernet ¶
The miscellaneous pin numbers 60-63 correspond to the CS5-CS8 pins on the expansion connector. These were originally allocated for use as the E2-E6 endstop pins and are labelled as such on the expansion connector, but they are now used to address thermocouple and RTD daughter boards on a DueX2 or DueX5 instead. Because most users don't need more than the four thermocouple and RTD channels supported on the Duet WiFi, we make CS5-8 available as general purpose I/O if you do not have any daughter boards fitted to the DueX2/X5. Here is the mapping between pin numbers, signal names, and the labels on the expansion connector:
| Logical pin | Signal name | Expansion connector label | Expansion connector pin number | PWM capable? | Servo capable? | Notes |
|---|---|---|---|---|---|---|
| 60 | CS5 | CS5 | 50 | no | no | |
| 61 | CS6 | E3_STOP | 9 | no | no | |
| 62 | CS7 | E4_STOP | 14 | no | no | |
| 63 | CS8 | E5_STOP | 19 | no | no | |
| 64 | ENC_SW | ENC_SW on CONN_SD connector | 7 on CONN_SD connector | no | no | |
| 65 | Z_PROBE_MOD | MOD on Z-probe connector | 3 on Z-probe connector | no | no | |
| 100-103 | GPIO pins 1-4 | yes | no | These are on the DueX2 and DueX5 expansion boards | ||
| 120-135 | SX1509B expansion I/O pins | yes | no | These are on an SX1509B-based expander board at I2C address 0x71 connected to a Duet 2 Wifi/Ethernet |
Logical pins 64 and 65 are supported in firmware 2.01 and later only. Note that the Z_PROB_MOD pin is driven automatically when some Z probe modes are selected.
Duet 2 Maestro ¶
| Logical pin | Signal name | Expansion connector label | Expansion connector pin number | PWM capable? | Servo capable? | Notes |
|---|---|---|---|---|---|---|
| 60 | PA21/RXD1/AD8 | no | no | |||
| 61 | PA22/TXD1/AD9 | no | no | |||
| 62 | PA3/TWD | no | no | |||
| 63 | PA4/TWC | no | no | |||
| 64 | Z_PROBE_MOD | MOD on Z_PROBE connector | ? on Z_PROBE connector | yes | yes |
Duet 0.6 and 0.8.5 ¶
The mapping between logical pin numbers for miscellaneous pins and the corresponding signal names on the expansion connector is as follows.
| Logical pin number | Expansion connector signal name |
|---|---|
| 60 | PA10/RXD0 |
| 61 | PA11/TXD0 |
| 62 | PA12/RXD1 |
| 63 | PA13/TXD1 |
| 64 | PA14/RTS1 |
| 65 | PB12/TWD1 |
| 66 | PB13/TWCK1 |
| 67 | PB16/DAC1 (also used as CS signal on external SD card socket) |
| 68 | PB21/AD14 |
| 69 | PC4 |
2 Comments
Dear David,
is there any information available for RADDS pin assignments.
There are three Servo pins available on a RADDS board, labeled as PWM1-3. But I can not really make out on how to call them in RRF notation.
Thanks for your help,
Andreas
Andreas Melzer - Reply
Hello,
I am looking to directly control the unused pins with C/C++ code (like an arduino). Is there a way to do this in the firmware or is there separate firmware I can load onto the Duet Wifi?
Thank You,
Caleb
caleb young - Reply