Bus Interface
5x
74LS148
10k
8
A8 – 15
0
0
0
D0 – D4
0
74LS365
0
/OE2
/OE1
/EI
/EO
/IORQULA
/RD
1k
External Keyboard Connector for ZX Spectrum
Circuit and Drawing 2006 kio@little-bat.de v.2
Keyboard
Cable
/IORQ
GS
/A /B /C
Adapter
74LS145
A B C D
8
0
0-7
0-7
8 9
5
5
5
ZX Spectrum
Notes:
the 1k resistor from /IORQ aids in pulling down the additional loads on /IORQ ULA. It is probably not required and may be omitted. The 74LS148 has inverted A/B/C outputs. Therefore the input lines A8 to A15 must be connected in reverse order to input 0 to 7 of the 74LS148.