Specification, RC2014 Bus

The RC2014 bus has evolved from a single inline set of pins suitable for construction on strip-board to a dual inline set of pins for more advanced modules.

Currently, the official specification for the bus defines a row of 40 pins, plus a partial row of 20 pins. The original 40-pin bus is referred to as the Standard bus, while the current version is referred to as the Enhanced bus. The Enhanced bus was first used on the RC2014 Pro backpane.

The various bus pin-outs are detailed below.

• Official Standard Bus
• Official Enhanced Bus
• Unofficial BP80 Bus
• Summary table
• SCxxx Uses of USER Pins

Electrical Specifications

There are no official electrical specifications for the bus. The nearest there is to a specification is that of the CMOS Z80 CMOS CPU which is directly connected to most bus pins. See Z80 datasheet for details.

Mechanical Specifications

<TODO>

Early RC2014 bus products had a variety of PCB sizes, but more recently they usually follow the official suggested board dimensions.

Official Standard Bus Pin-outs

The Standard Bus contains only a single row of pins. The second row, added later, is simply not present on the Standard Bus.

Pins labelled “USER” can be used by anyone for any purpose.

Row 2 Pin #	Second Row Not present		Row 1 Pin #	Standard Bus Signal Name
1			1	A15
2			2	A14
3			3	A13
4			4	A12
5			5	A11
6			6	A10
7			7	A9
8			8	A8
9			9	A7
10			10	A6
11			11	A5
12			12	A4
13			13	A3
14			14	A2
15			15	A1
16			16	A0
17			17	GND
18			18	5V
19			19	/M1
20			20	/RESET
21			21	CLK
22			22	/INT
23			23	/MREQ
24			24	/WR
25			25	/RD
26			26	/IORQ
27			27	D0
28			28	D1
29			29	D2
30			30	D3
31			31	D4
32			32	D5
33			33	D6
34			34	D7
35			35	TX
36			36	RX
37			37	USER1
38			38	USER2
39			39	USER3
40			40	USER4

Official Enhanced Bus Pin-outs

The Enhanced Bus is essentially a Standard RC2014 Bus with a partial second row added. The pins named “Not used” are actually not present on the Pro backplane.

Row 2 Pin #	Enhanced Bus Signal Name		Row 1 Pin #	Standard Bus Signal Name
1	Not used		1	A15
2	Not used		2	A14
3	Not used		3	A13
4	Not used		4	A12
5	Not used		5	A11
6	Not used		6	A10
7	Not used		7	A9
8	Not used		8	A8
9	Not used		9	A7
10	Not used		10	A6
11	Not used		11	A5
12	Not used		12	A4
13	Not used		13	A3
14	Not used		14	A2
15	Not used		15	A1
16	Not used		16	A0
17	GND		17	GND
18	5V		18	5V
19	/RFSH		19	/M1
20	PAGE or /RESET2		20	/RESET
21	CLK2		21	CLK
22	/BUSAK		22	/INT
23	/HALT		23	/MREQ
24	/BUSRQ		24	/WR
25	/WAIT		25	/RD
26	/NMI		26	/IORQ
27	D8		27	D0
28	D9		28	D1
29	D10		29	D2
30	D11		30	D3
31	D12		31	D4
32	D13		32	D5
33	D14		33	D6
34	D15		34	D7
35	TX2		35	TX
36	RX2		36	RX
37	USER5		37	USER1
38	USER6		38	USER2
39	USER7		39	USER3
40	USER8		40	USER4

Unofficial Backplane-80 Pin-outs

This unofficial variant of the RC2014 Bus was introduced in order to make a universal 80-pin modular backplane and to allow extra signals for future modules, such as the Z180 CPU.

Pins labelled “custom” are available for allocation as needed for individual products or applications.

Row 2 Pin #s	Signal Name		Row 1 Pin #	Signal Name
41	#41 (custom)		1	A15
42	#42 (custom)		2	A14
43	#43 (custom)		3	A13
44	#44 (custom)		4	A12
45	#45 (custom)		5	A11
46	#46 (custom)		6	A10
47	#47 (custom)		7	A9
48	#48 (custom)		8	A8
49	A23		9	A7
50	A22		10	A6
51	A21		11	A5
52	A20		12	A4
53	A19		13	A3
54	A18		14	A2
55	A17		15	A1
56	A16		16	A0
57	GND		17	GND
58	5V		18	5V
59	/RFSH		19	/M1
60	PAGE		20	/RESET
61	CLK2		21	CLK
62	/BUSAK		22	/INT
63	/HALT		23	/MREQ
64	/BUSRQ		24	/WR
65	/WAIT		25	/RD
66	/NMI		26	/IORQ
67	#67 (custom)		27	D0
68	#68 (custom)		28	D1
69	#69 (custom)		29	D2
70	#70 (custom)		30	D3
71	#71 (custom)		31	D4
72	#72 (custom)		32	D5
73	#73 (custom)		33	D6
74	#74 (custom)		34	D7
75	TX2		35	TX
76	RX2		36	RX
77	USER5		37	USER1
78	USER6		38	USER2
79	USER7		39	USER3
80	USER8 (IEI)		40	USER4 (IEO)

Bus pins USER8 and USER4 are used as a Z80 mode 2 interrupt daisy chain, so are not wired straight through link the other signals. Instead USER4 of one socket is connected to USER8 of the next, forming a daisy chain.

Summary

The following table summarises the variants of the RC2014 based buses.

• RC40 is the RC2014 Standard bus
• RC64 is the RC2014 Pro bus
• RC80 is an unofficial extended bus
• BP80 is an unofficial extended bus with two of the USER pins wired as an interrupt daisy-chain

Row 1
Pin	Signal	RC40	RC64	RC80	BP80
1	A15	•	•	•	•
2	A14	•	•	•	•
3	A13	•	•	•	•
4	A12	•	•	•	•
5	A11	•	•	•	•
6	A10	•	•	•	•
7	A9	•	•	•	•
8	A8	•	•	•	•
9	A7	•	•	•	•
10	A6	•	•	•	•
11	A5	•	•	•	•
12	A4	•	•	•	•
13	A3	•	•	•	•
14	A2	•	•	•	•
15	A1	•	•	•	•
16	A0	•	•	•	•
17	GND	•	•	•	•
18	5V	•	•	•	•
19	/M1	•	•	•	•
20	/RESET	•	•	•	•
21	CLK	•	•	•	•
22	/INT	•	•	•	•
23	/MREQ	•	•	•	•
24	/WR	•	•	•	•
25	/RD	•	•	•	•
26	/IORQ	•	•	•	•
27	D0	•	•	•	•
28	D1	•	•	•	•
29	D2	•	•	•	•
30	D3	•	•	•	•
31	D4	•	•	•	•
32	D5	•	•	•	•
33	D6	•	•	•	•
34	D7	•	•	•	•
35	TX	•	•	•	•
36	RX	•	•	•	•
37	USER1	•	•	•	•
38	USER2	•	•	•	•
39	USER3	•	•	•	•
40	USER4 IEO	•	•	•	•
Row 2
Pin	Signal	RC40	RC64	RC80	BP80
41	#41 (custom)			•	•
42	#42 (custom)			•	•
43	#43 (custom)			•	•
44	#44 (custom)			•	•
45	#45 (custom)			•	•
46	#46 (custom)			•	•
47	#47 (custom)			•	•
48	#48 (custom)			•	•
49	A23			•	•
50	A22			•	•
51	A21			•	•
52	A20			•	•
53	A19			•	•
54	A18			•	•
55	A17			•	•
56	A16			•	•
57	GND		•	•	•
58	5V		•	•	•
59	/RFSH		•	•	•
60	PAGE /RESET2		• •	• •	•
61	CLK2		•	•	•
62	/BUSAK		•	•	•
63	/HALT		•	•	•
64	/BUSRQ		•	•	•
65	/WAIT		•	•	•
66	/NMI		•	•	•
67	D8 #67 (custom)		•	•	•
68	D9 #68 (custom)		•	•	•
69	D10 #69 (custom)		•	•	•
70	D11 #70 (custom)		•	•	•
71	D12 #71 (custom)		•	•	•
72	D13 #72 (custom)		•	•	•
73	D14 #73 (custom)		•	•	•
74	D15 #74 (custom)		•	•	•
75	TX2		•	•	•
76	RX2		•	•	•
77	USER5		•	•	•
78	USER6		•	•	•
79	USER7		•	•	•
80	USER8 IEI		•	•	•

SCxxx Uses of USER, TX, RX and ‘custom’ pins

My SCxxx range use the bus pins as described above (unofficial backplane-80 pin-outs). Any uses of USER, TX, RX, and ‘custom’ pins are indicated below.

Design	Uses of USER, TX and RX Pins
SC101 v1.0 Z80 Motherboard	None
SC102 v1.1 Z80 CTC module	USER1 = CTC 3 input (optional via jumper) USER2 = IEI input (optional via jumper) USER3 = IEO output (optional via jumper) USER5 = CTC 0 input (optional via jumper) USER6 = CTC 1 input (optional via jumper) USER7 = CTC 2 input (optional via jumper)
SC103 v1.0 Z80 PIO module	USER2 = IEI input (optional via jumper) USER3 = IEO output (optional via jumper)
SC104 v1.0 Z80 SIO/2 module	USER2 = IEI input (optional via jumper) USER3 = IEO output (optional via jumper) TX = Port A output (optional via jumper) RX = Port A input (optional via jumper) TX2 = Port B output (optional via jumper) RX2 = Port B input (optional via jumper)
SC105 v1.0 Modular backplane	USER4 = IEO (interrupt daisy chain) USER8 = IEI (interrupt daisy chain)
SC106 v1.0 Modular backplane	USER4 = IEO (interrupt daisy chain) USER8 = IEI (interrupt daisy chain)
SC107 v1.0 Modular backplane	USER2 = IEI (interrupt daisy chain) USER3 = IEO (interrupt daisy chain) USER4 = IEO (interrupt daisy chain) USER8 = IEI (interrupt daisy chain)
SC108 v1.0 Z80 CPU module	None
SC109 v1.0 Modular backplane	USER4 = IEO (interrupt daisy chain) USER8 = IEI (interrupt daisy chain)
SC110 v1.0 Z80 SIO/2 + CTC module	USER1 = CTC 3 input (optional via jumper) USER2 = IEI input (optional via jumper) USER3 = IEO output (optional via jumper) USER5 = CTC 0 input (optional via jumper) TX = Port A output (TXA) RX = Port A input (RXA) TX2 = Port B output (TXB) RX2 = Port B input (RXB)
SC111 v1.0 Z180 CPU module	USER1 = INT 1 input (optional via jumper) TX = Port A output (optional via jumper) RX = Port A input (optional via jumper) TX2 = Port B output (optional via jumper) RX2 = Port B input (optional via jumper)
SC112 v1.0 Modular backplane	USER4 = IEO (interrupt daisy chain) USER8 = IEI (interrupt daisy chain) Daisy chain IEI/IEO possible on USER2/3 via links. USER1, 2, 3 TX2 and RX2 can be isolated via jumpers between some sockets.
SC113 v1.1 Modular backplane	USER4 = IEO (interrupt daisy chain) USER8 = IEI (interrupt daisy chain) Daisy chain IEI/IEO possible on USER2/3 via links. USER1, 2, 3 TX2 and RX2 can be isolated via jumpers between some sockets.
SC114 v1.0 Z80 Motherboard	None
SC115 v1.0 Breakout module	None committed All signals available on headers
SC116 v1.0 Backplane (3-slot)	USER4 = IEO (interrupt daisy chain) USER8 = IEI (interrupt daisy chain)
SC119 v1.0 Z180 Memory module	None
SC126 v1.0 Z180 Motherboard	USER4 = IEO (interrupt daisy chain) USER6 = I2C SCL (optional via jumper) USER7 = I2C SDA (optional via jumper) USER8 = IEI (interrupt daisy chain) TX = Port A output (TXA) RX = Port A input (RXA) TX2 = Port B output (TXB) RX2 = Port B input (RXB)