The I/O board

This is the I/O board for the I/O bus (see specs for I/O bus below).
 
The first 128 I/O ports (00h-7fh) are reserved for internal reZet80 use.
They are divided into 8 regions of 16 ports each by a demultiplexer:

00h-0fh, 10h-1fh, 20h-2fh, 30h-3fh, 40h-4fh, 50h-5fh, 60h-6fh and 70h-7fh.

The 8 regions will be further subdivided on demand.

8 LEDs flash while the corresponding I/O region is selected.

The remaining 128 I/O ports are free to use: 80h-ffh.

reZet80 I/O bus:
IOB01: D7
IOB02: D6
IOB03: D5
IOB04: D4
IOB05: D3
IOB06: D2
IOB07: D1
IOB08: D0
IOB09: IOREQ
IOB10: MREQ
IOB11: NMI
IOB12: INT
IOB13: RD
IOB14: WR
IOB15: BUSACK
IOB16: WAIT
IOB17: BUSREQ
IOB18: RESET
IOB19: M1
IOB20: RFSH
IOB21: GND
IOB22: +5V
IOB23: A0
IOB24: A1
IOB25: A2
IOB26: A3
IOB27: A4
IOB28: A5
IOB29: A6
IOB30: A7
IOB31: IOSEL_00_0F
IOB32: IOSEL_10_1F
IOB33: IOSEL_20_2F
IOB34: IOSEL_30_3F
IOB35: IOSEL_40_4F
IOB36: IOSEL_50_5F
IOB37: IOSEL_60_6F
IOB38: IOSEL_70_7F
IOB39: CLK
IOB40: HALT

Bill of materials:
- PCB 5x7 cm (at least 22 rows)
- 22-pin right-angled male connector
- 8-pin male connector
- DIP-16 socket
- DIP-20 socket
- 74x138 demultiplexer
- 74x240 octal buffer
- 8x LED red
- 8x resistor 220R (choose according to the LED specs)
- capacitor 100 nF