Pin alternate functions (multiplexing)
All 32 I/Os work as general-purpose analog or digital pins. Fourteen of them can also be switched to a dedicated communication interface, and those interfaces share pins, so enabling one takes its pins away from the others. The table below is the single place that mapping is recorded: read down a column to see which GPIOs an interface consumes, or across a row to see what a given pin can become.
When a pin is used for a dedicated communication interface, it cannot be used as a general-purpose I/O, and more importantly, it cannot support the high voltage range of regular I/Os (-25 V to +25 V). Disabling the communication interface will restore the pin to its original I/O function and voltage range.
All alternate functions​
| GPIO | SPI | I2C | UART | JTAG * | SWD * | CAN | RS485 | RS232 |
|---|---|---|---|---|---|---|---|---|
| DA0-DA15 | ||||||||
| DA16 | MOSI_0 | SDA_0 | RX_0 | TDI_0 | SWDIO_0 | |||
| DA17 | MISO_0 | TDO_0 | ||||||
| DA18 | SCK_0 | SCL_0 | TX_0 | TCK_0 | SWCLK_0 | |||
| DA19 | TMS_0 | |||||||
| DA20 | MOSI_1 | SDA_1 | RX_1 | TDI_1 | SWDIO_1 | |||
| DA21 | MISO_1 | TDO_1 | ||||||
| DA22 | SCK_1 | SCL_1 | TX_1 | TCK_1 | SWCLK_1 | |||
| DA23 | TMS_1 | |||||||
| DA24 | CANH | A(+) 0 | ||||||
| DA25 | CANL | B(-) 0 | ||||||
| DA26 | A(+) 1 | |||||||
| DA27 | B(-) 1 | |||||||
| DA28 | TX | |||||||
| DA29 | RX | |||||||
| DA30-31 |
DA0 to DA15 and DA30 to DA31 have no alternate function and are always available as general-purpose I/O.
What this costs you​
Reading the table by interface:
| Interface | Pins it takes | Also blocks |
|---|---|---|
| SPI 0 | DA16, DA17, DA18 | I2C 0, UART 0, JTAG 0, SWD 0 |
| SPI 1 | DA20, DA21, DA22 | I2C 1, UART 1, JTAG 1, SWD 1 |
| I2C 0 | DA16, DA18 | SPI 0, UART 0, JTAG 0, SWD 0 |
| I2C 1 | DA20, DA22 | SPI 1, UART 1, JTAG 1, SWD 1 |
| UART 0 | DA16, DA18 | SPI 0, I2C 0, JTAG 0, SWD 0 |
| UART 1 | DA20, DA22 | SPI 1, I2C 1, JTAG 1, SWD 1 |
| CAN 0 | DA24, DA25 | RS485 0 |
| RS485 0 | DA24, DA25 | CAN 0 |
| RS485 1 | DA26, DA27 | - |
| RS232 | DA28, DA29 | - |
So SPI, I2C and UART on the same index are mutually exclusive, and CAN shares its pins with RS485 0. Everything else can run at the same time. RS232 has dedicated pins and never conflicts.
JTAG and SWD are not currently supported and will be implemented in a future release. The AT1000 device is designed to support JTAG and SWD protocols, but the implementation is not yet available in the current version of the API. Please check back for updates on this feature.
An RS422 interface can be implemented by combining the two available RS485 interfaces. One pair (A(+) and B(-)) can be used for transmitting data, while the other pair (A(+) and B(-)) can be used for receiving data.
Enabling an interface configures its pins automatically. Attempting to enable two
interfaces that share pins raises an error at configure(), so a conflict shows up as
soon as you run the script rather than as puzzling behaviour on the bench.