b68k-io

IO extension board for b68k computer.

Features

• 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 set

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