MCA 32 bit bus
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MCA 32 bit bus

pinout

plus MCA memory-matched extensions, MCA AVEC Auxiliary Video Extension Connector

172 pin MCA bus
172 pin MCA bus connector  at the motherboard

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 ISA"s 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 ID"s 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 didn"t 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
B01AUDIO GNDA01-CD SETUP
B02AUDIOA02MADE 24
B03GNDA03GND
B0414.3 MHz OSZA04A11
B05GNDA05A10
B06A23A06A09
B07A22A07+5 Vdc
B08A21A08A08
B09GNDA09A07
B10A20A10A06
B11A19A11+5 Vdc
B12A18A12A05
B13GNDA13A04
B14A17A14A03
B15A16A15+5 Vdc
B16A15A16A02
B17GNDA17A01
B18A14A18A00
B19A13A19+12 Vdc
B20A12A20-ADL
B21GNDA21-PREEMPT
B22-IRQ 09A22-BURST
B23-IRQ 03A23-12 Vdc
B24-IRQ 04A24ARB 00
B25GNDA25-ARB 01
B26-IRQ 05A26ARB 02
B27-IRQ 06A27-12 Vdc
B28-IRQ 07A28ARB 03
B29GNDA29ARB/-GNT
B30-DPARENA30-TC
B31DPAR(0)A31+5 Vdc
B32-CHCKA32-SO
B33GNDA33-S1
B34-CMDA34M/-IO
B35CHRDYRTNA35+12 Vdc
B36-CD SFDA36CD CHRDY
B37GNDA37D 0
B38D 01A38D 02
B39D 03A39+5 Vdc
B40D 04A40D 05
B41GNDA41D 06
B42CHRESETA42D 07
B43-SD STROBEA43GND
B44-SDR (0)A44-DS 16 RTN
B45GNDA45-REFRESH
B46- key -A46- key -
B47- key -A47- key -
B48D 08A48+5 Vdc
B49D 09A49D 10
B50GNDA50D 11
B51D 12A51D 13
B52D 14A52+12 Vdc
B53D 15A53DPAR(1)
B54GNDA54-SBHE
B55-IRQ 10A55-CD DS 16
B56-IRQ 11A56+5 Vdc
B57-IRQ 12A57-IRQ 14
B58GNDA58-IRQ 15
B59reservedA59reserved
B60reservedA60reserved
Pin32-bit bus
Signal Name
Pin32-bit bus
Signal Name
B61-SDR(1)A61GND
B62-MSDRA62reserved
B63GNDA63reserved
B64D 16A64-SFDBKRTN
B65D 17A65+12 Vdc
B66D 18A66D 19
B67GNDA67D 20
B68D 22A68D 21
B69D 23A69+5 Vdc
B70DPAR(2)A70D 24
B71GNDA71D 25
B72D 27A72D 26
B73D 28A73+5 Vdc
B74D 29A74D 30
B75GNDA75D 31
B76-BE 0A76DPAR(3)
B77-BE 1A77+12 Vdc
B78-BE 2A78-BE 3
B79GNDA79-DS 32 RTN
B80TR 32A80-CD DS 32
B81A 24A81+5 Vdc
B82A 25A82A 26
B83GNDA83A 27
B84A 29A84A 28
B85A 30A85+5 Vdc
B86A 31A86-APAREN
B87GNDA87-APAR(0)
B88APAR(2)A88-APAR(1)
B89APAR(3)A89GND

MCA memory-matched extensions - pin AM1-BM1 / pin AM4-BM4
Pin Signal Name Pin Signal Name
BM4GroundAM4Reserved
BM3ReservedAM3-MMC_CMD
BM2-MMCRAM2Ground
BM1ReservedAM1-MMC

MCA AVEC Auxiliary Video Extension Connector - pin BV1-AV1 / pin BV10-BV10
Pin Signal Name Pin Signal Name
BV10ESYNCAV10VSYNC
BV9GroundAV9HSYNC
BV8P5AV8BLSNK
BV7P4AV7Ground
BV6P3AV6P6
BV5GroundAV5EDCLK
BV4P2AV4DCLK
BV3P1AV3Ground
BV2P0AV2P7
BV1GroundAV1EVIDEO

Source:www.pinouts.ru


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