IO extension board for b68k computer.
- local bus peripheral to b68k-cpu computer
- a UART with DB9 connector (RS232, no hardware flow control)
- an I2C bus with onboard RTC chip (DS1307+) with crystal and backup battery, and 4-pins pin header extension connector
- a SPI bus with 7 chip select lines: 2x SD cards slots, 1x through an 8-pins pin header extension connector, 4x through DB15 connector for external equipements (external SPI slaves are electrically isolated from internal slaves)
Board fonctions are implemented with a PIC18F27K42 microcontroller.
The board has only two memory locations accessible through the expansion bus: one to set the actual register to access, the other to read or write data from/to the register.
| register | address | description |
|---|---|---|
| DATA | XX0000h | register data |
| ADDRESS | XX0001h | register index |
| register | index | description |
|---|---|---|
| SPI_SEL | 0 | [5..3] : enabled SPI chip select line 0: external #0 1: external #1 2: external #2 3: external #3 4: SD card A 5: SD card B 6: internal pin header 7: none (reset) |
| SPI_CTRL | 1 | bit 7: BUSY r bit 2: CLRBF s bit 1: TXR rw bit 0: RXR rw |
| SPI_DATA | 2 | SPI data in/out |
| UART_STS | 4 | UART status bit 7: TX ready bit 1: RX FIFO overflow bit 0: RX FIFO underflow |
| UART_DATA | 5 | UART data in/out |
| I2C_CTRL | 6 | bit 7: RXIF bit 5: TXBE bit 2: reset bit 1: start bit 0: RXBF |
| I2C_CNT | 7 | |
| I2C_DATA | 8 | |
| I2C_CMD | 9 | bit 7..1: address bit 0: RWn |
| IRQCFG | 14 | interrupt controller configuration bit 0: enable UART RX interrupt |
| IRQSTS | 15 | interrupt controller status bit 0: UART RX interrupt pending |