ZX Spectrum +3 / +2A Expansion Bus
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PIN	UPPER ROW	LOWER ROW

1	A15		A14
2	A13		A12
3	D7    		+5V
4	!ROM1_OE	not used
5	D0		GND
6	D1		GND
7	D2		CK
8	D6		A0
9	D5		A1
10	D3		A2
11	D4		A3
12	!INT		not used
13	!NMI		GND
14	!HALT		!ROM2_OE
15	!MREQ		!DISK_RD
16	!IORQ		!DISK_WR
17	!RD		!MOTOR_ON
18	!WR		!BUSRQ
19	not used	!RESET
20	!WAIT		A7
21	+12V		A6
22	-12V		A5
23	!M1		A4
24	!RFSH		not used
25	A8		BUSACK
26	A10		A9
27	RESET		A11