The processor acts as a DCE. Accordingly, the terminal devices on the SIO 0/1 ports (controllers, memory cards, modem, data-link receiver) act as DTEs.
| Signal | Description |
|---|---|
| Signal group for controller/memory card ports | |
| /INTIN10 | SIO interrupt; Combined with PIO interrupt (most likely via pullup resistor, as is ordinary) |
| /DSR0 | Data Set Ready. DCE is ready to receive and send data. |
| /DTR0B | Data Terminal Ready. DTE is ready to receive, initiate, or continue a call (Port B) |
| /DTR0A | Data Terminal Ready. DTE is ready to receive, initiate, or continue a call (Port A) |
| RXD0 | Received Data. Carries data from DCE to DTE (Controllers/Memcards) |
| TXD0 | Transmitted Data. Carries data from DTE to DCE (Controllers/Memcards) |
| /SCK0 | Controllers/memory cards do not use ordinary start/stop bit communication. Instead, Serial CLK is used. |
| Signal group for SIO port | |
| RXD1 | Received Data. Carries data from DCE to DTE (SIO port) |
| TXD1 | Transmitted Data. Carries data from DTE to DCE (SIO port) |
| /DSR1 | Data Set Ready. DCE is ready to receive and send data (SIO port) |
| /DTR1 | Data Terminal Ready. DTE is ready to receive, initiate, or continue a call (SIO port) |
| /CTS1 | Clear To Send. DCE is ready to accept data from the DTE (SIO port) |
| /RTS1 | Request To Send. DTE requests the DCE prepare to transmit data (SIO port) |
