MCA 32 bit bus pinout

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Micro Channel architecture (in practice almost always shortened to MCA) was a proprietary 16 or 32-bit parallel computer bus created by IBM in the 1980s for use on their new PS/2 computers. For a time MCA could be found in the PS/2, RS/6000, AS/400 and even some of the System/370 mainframes. However all of these later moved on to more capable, standards based, busses (such as PCI) and MCA is no longer used.

MCA was primarily a 32-bit bus, but the system also supported a 16-bit mode which was primarily to lower the cost of connectors and logic in Intel-based machines like the PS/2. The situation was never that simple however, as both the 32-bit and 16-bit versions had a number of additional optional connectors which resulted in a huge number of physically incompatible cards. On the upside, MCA also moved the pins around to minimize interference, a ground or a supply was located within 3 pins of every signal.

The data rate was increased from ISAs 8MHz to 10, for a small improvement in performance. However the communications was now driven by the bus as opposed to the CPU, so real throughput was greatly increased, about four times, to 40MBps (of a theoretical 66). With bus-mastering the card could talk to each other directly so the performance was independent of the CPU. This led to possible collisions when more than one card would try to master, but MCA included an arbitration feature to correct for these situations, and also allowed a master to use a burst-mode where they had complete control for up to 12 milliseconds. Multiple busmaster support and improved arbitration means that several such devices can coexist and share the system bus. MCA busmasters can even use the bus to talk directly to each other at speeds faster than the system CPU, without any other system intervention. Arbitration enhancement also provides that we have better system throughput since control is passed more efficiently. Advanced interrupt handling refers to the use of level sensitive interrupts to handle system requests. Rather than a dedicated interrupt line, several lines can be shared to provide more possible interrupts. The final major improvement was POS, the Programmable Option Select, which allowed all setup to take place in software. This feature is taken for granted now, but at the time setup was a huge chore for ISA systems. POS was a simple system that included device IDs in firmware, which the drivers in the computer were supposed to interpret. This is the basis of plug-and-play today.

Although MCA was a huge improvement over ISA, it was limited only to IBM hardware. It was not compatible with either EISA or XT bus architecture so older cards cannot be used with it. This small market made for very high prices, and IBM didnt help matters by charging high licensing fees. MCA was largely ignored, and with the introduction of PCI, MCA swiftly disappeared.

Pin	Signal Name	Pin	Signal Name
B01	AUDIO GND	A01	-CD SETUP
B02	AUDIO	A02	MADE 24
B03	GND	A03	GND
B04	14.3 MHz OSZ	A04	A11
B05	GND	A05	A10
B06	A23	A06	A09
B07	A22	A07	+5 Vdc
B08	A21	A08	A08
B09	GND	A09	A07
B10	A20	A10	A06
B11	A19	A11	+5 Vdc
B12	A18	A12	A05
B13	GND	A13	A04
B14	A17	A14	A03
B15	A16	A15	+5 Vdc
B16	A15	A16	A02
B17	GND	A17	A01
B18	A14	A18	A00
B19	A13	A19	+12 Vdc
B20	A12	A20	-ADL
B21	GND	A21	-PREEMPT
B22	-IRQ 09	A22	-BURST
B23	-IRQ 03	A23	-12 Vdc
B24	-IRQ 04	A24	ARB 00
B25	GND	A25	-ARB 01
B26	-IRQ 05	A26	ARB 02
B27	-IRQ 06	A27	-12 Vdc
B28	-IRQ 07	A28	ARB 03
B29	GND	A29	ARB/-GNT
B30	-DPAREN	A30	-TC
B31	DPAR(0)	A31	+5 Vdc
B32	-CHCK	A32	-SO
B33	GND	A33	-S1
B34	-CMD	A34	M/-IO
B35	CHRDYRTN	A35	+12 Vdc
B36	-CD SFD	A36	CD CHRDY
B37	GND	A37	D 0
B38	D 01	A38	D 02
B39	D 03	A39	+5 Vdc
B40	D 04	A40	D 05
B41	GND	A41	D 06
B42	CHRESET	A42	D 07
B43	-SD STROBE	A43	GND
B44	-SDR (0)	A44	-DS 16 RTN
B45	GND	A45	-REFRESH
B46	- key -	A46	- key -
B47	- key -	A47	- key -
B48	D 08	A48	+5 Vdc
B49	D 09	A49	D 10
B50	GND	A50	D 11
B51	D 12	A51	D 13
B52	D 14	A52	+12 Vdc
B53	D 15	A53	DPAR(1)
B54	GND	A54	-SBHE
B55	-IRQ 10	A55	-CD DS 16
B56	-IRQ 11	A56	+5 Vdc
B57	-IRQ 12	A57	-IRQ 14
B58	GND	A58	-IRQ 15
B59	reserved	A59	reserved
B60	reserved	A60	reserved
Pin	32-bit bus Signal Name	Pin	32-bit bus Signal Name
B61	-SDR(1)	A61	GND
B62	-MSDR	A62	reserved
B63	GND	A63	reserved
B64	D 16	A64	-SFDBKRTN
B65	D 17	A65	+12 Vdc
B66	D 18	A66	D 19
B67	GND	A67	D 20
B68	D 22	A68	D 21
B69	D 23	A69	+5 Vdc
B70	DPAR(2)	A70	D 24
B71	GND	A71	D 25
B72	D 27	A72	D 26
B73	D 28	A73	+5 Vdc
B74	D 29	A74	D 30
B75	GND	A75	D 31
B76	-BE 0	A76	DPAR(3)
B77	-BE 1	A77	+12 Vdc
B78	-BE 2	A78	-BE 3
B79	GND	A79	-DS 32 RTN
B80	TR 32	A80	-CD DS 32
B81	A 24	A81	+5 Vdc
B82	A 25	A82	A 26
B83	GND	A83	A 27
B84	A 29	A84	A 28
B85	A 30	A85	+5 Vdc
B86	A 31	A86	-APAREN
B87	GND	A87	-APAR(0)
B88	APAR(2)	A88	-APAR(1)
B89	APAR(3)	A89	GND

MCA memory-matched extensions - pin AM1-BM1 / pin AM4-BM4

MCA AVEC Auxiliary Video Extension Connector - pin BV1-AV1 / pin BV10-BV10