ZX Spectrum BUS   versus   Russian ZX-BUS (NEMO-BUS)

System connector on ZX Sprectrum		ZX-BUS (russian NEMO-BUS)	
Signal	top	bottom	Signal		Signal	top	bottom	Signal	
A15	1U	1L	A14		A15	1B	1А	A14	
A13	2U	2L	A12		A13	2B	2A	A12	
D7	3U	3L	+5V		D7	3B	3A	+5V	
	4U	4L	+9V		BLK	4B	4A	/DOS	
					TURBO	5B	5A	F	
D0	5U	5L	GND		D0	6B	6A	GND	
D1	6U	6L	GND		D1	7B	7A	GND	
D2	7U	7L	CLK		D2	8B	8A	CLK	
D6	8U	8L	A0		D6	9B	9A	A0	
D5	9U	9L	A1		D5	10B	10A	A1	
D3	10U	10L	A2		D3	11B	11A	A2	
D4	11U	11L	A3		D4	12B	12A	A3	
/INT	12U	12L	/IORQE		/INT	12B	13A	/IORQGE	
/NMI	13U	13L	GND		/NMI	14B	14A	GND	
/HALT	14U	14L	VIDEO		/HALT	15B	15A	/RDR	
/MREQ	15U	15L	Y		/MREQ	16B	16A	RS	
/IORQ	16U	16L	V		/IORQ	17B	17A		
/RD	17U	17L	U		/RD	18B	18A		
/WR	18U	18L	/BUSRQ		/WR	19B	19A	/BUSRQ	
-5V	19U	19L	/RESET			20B	20A	/RESET	
/WAIT	20U	20L	A7		/WAIT	21B	21A	A7	
+12V	21U	21L	A6			22B	22A	A6	
-12V	22U	22L	A5			23B	23A	A5	
/M1	23U	23L	A4		/M1	24B	24A	A4	
/RFSH	24U	24L	/ROMCS		/RFSH	25B	25A	/CSROM	
A8	25U	25L	/BUSAK		A8	26B	26A	/BUSAK	
A10	26U	26L	A9		A10	27B	27A	A9	
	27U	27L	A11		+5V	28B	28A	A11	
					+12V	29B	29A	+5V	
					GND	30B	30A	GND	

F – main oscillator speed (signal 14 MHz)

BLK (DCGE) - info about memory in low 16kB ( 0=rom / 1=ram )

/DOS - info about TR-DOS activity: 0=DOS is active, 1-DOS inactive

/CSROM (/CSR) – disable ROM (0=cpu read from rom / 1=rom unused)

/RDR (/RDROM, /CRGE, /CSROMGE) – signal for disable read from internal ROM. Set /RDR to log.1 disable /ROMOE on ROM chip. (ula can active ROM via /CSROM=0, but this signal disable data output)

RS (ROMSEL) - ROM type (D4 of port #7FFD)

/IORQGE (/IORGE, /IOGE) – similar signal as on ZX Spectrum BUS. Set to log.1 disable internal I/O ports and external interface can use this ports for any other functions. Pentagon 1024 contain three ZX-BUS connectors and use different IORQGE priority for each BUS connector. ZX-BUS1 use high priority, ZX-BUS2 low priotity ald ZX-BUS3 lower priority. For example: if you connect three interfaces and each device will use IORQGE signal, then interface in ZX-BUS1 will access always as first.

TURBO – CPU speed detection: 0=3.5MHz / 1=TURBO