mca bus operations

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22MCA BUS

OPERATIONS

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CONTENTS AT A GLANCE

MCA Bus Configuration and SignalsMCA layout

Knowing the MCA signals

PS/2 Reference and Diagnostic DisksClearing a 55SX password

Dealing with PS/2 165 errors

(.ADF files)

General Bus Troubleshooting

Further StudyUsenet newsgroup

With the introduction and widespread use of 32-bit microprocessors, such as the Intel80386 and 80486, the 16-bit ISA bus faced a serious data throughput bottleneck. Passing

a 32-bit word across the expansion bus in two 16-bit halves presented a serious waste of

valuable processing time. Not only was data and CPU speed an issue, but video and audio

systems in PCs had also been improvingand demanding an increasing share of bus

bandwidth. By early 1987, IBM concluded that it was time to lay the ISA bus to rest andunleash an entirely new bus structure, which it dubbed the MicroChannel Architecture

(MCA). IBM incorporated the MCA bus into their PS/2 series of personal computers and

also in their System/6000 workstations. This chapter shows you the layout and operations

of the MCA bus.


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MCA Bus Configuration and SignalsAll things considered, the MCA bus was a revolutionaryand superiordesign. One ofthe most substantial advantages is a reduction in electrical noise because of a radical re-

arrangement of bus signals. Unlike the ISA or EISA bus (which had only a few ground

lines), the MCA bus provides an electrical ground every fourth pin. Superior grounding

and the corresponding reduction in electrical interference also means that the MCA bus

can operate at higher frequencies than XT or AT busses (10MHz, as opposed to the

ISA/EISA 8.33MHz). The MCA bus also offers extended performance in data and ad-

dressing. You already know that an MCA bus can work with up to 32-bits of data. How-

ever, the bus also has an increased number of address lines (32 instead of 24). This

increases the amount of directly addressable memory from 16MB to 4GB.

The MCA also brings sound and video to the bus. A single analog audio channel is

added to the 8-bit bus segment. The audio channel can handle voice and music, and is in-tended to be almost as good as FM radio (roughly about 50Hz to 10kHz). Because the au-

dio channel is available to all expansion devices, the signal can be exchanged and

processed among each device independently. A VGA video extension is also provided

with the MCA bus. This allows expansion video boards to be installed and work in con-

cert with the VGA circuitry already existing on the MCA motherboard. An 8-bit video

data bus and all necessary synchronization signals are available to an expansion board.

Typically, only one video extension connector is included on an MCA motherboard.

Still more advances include such features as matched memory cycles, burst and stream-

ing data modes, data multiplexing, and bus mastering. A matched memory cycle is sup-

ported with a small expansion connector. When a device is capable of sustaining matched

memory transfers, the typical memory transfer cycle of 250 ns is increased 25% to only

187 ns. The burst data-transfer mode allows data to be transferred in blocks without the

intervention of a CPU (unlike ordinary data transfers, which require multiple CPU cyclesfor each transfer). The streaming data-transfer mode allows even faster transfers during

bus-mastering operation. Using a data multiplexing technique, the MCA bus can accom-

plish 64-bit data transfers by multiplexing the upper 32 data bits on the 32 idle address

lines. Finally, the MCA bus supports bus masteringa technique that allows other de-

vices besides the main CPU to take control of the system busses to accomplish their re-

spective tasks.

Although MCA offers many tangible enhancements over the ISA bus, computer users

refused to abandon their hardware and software investment in order to scramble for lim-

ited MCA-compatible peripherals to fill their needs. As a result, the MCA bus has never

become the new standard that IBM hoped it would be. Although the number of PS/2 sys-

tems still in service are dwindling rapidly, you might still encounter PS/2s in many home

and school environments.

MCA LAYOUT

The layout for an MCA bus slot is shown in Fig. 22-1. Notice that up to three segments

are on the bus connector: an 8-bit portion, a 16-bit portion, and a 32-bit portion. Also, an

auxiliary video extension connector is usually available on only one slot. The first thing

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you should realize about the MCA bus is that it is physically much smaller than an ISA or

EISA busas a result, it is totally incompatible with ISA or EISA expansion products.

The pinout for a 16-bit MCA slot is shown in Table 22-1. This primary type of MCAconnector combines video and audio signals in the expansion bus. The connection itself

can be divided into three sections: the video section (pins xV00 to xV10), the 8-bit section

(pins 1 through 45), and the 16-bit section (pins 48 to 58). Power, ground, and interrupt

lines are easy to spot, but most other signals are new. The signal pinout for a 32-bit MCA

slot is shown in Table 22-2. The 32-bit bus replaces the video section with a smaller

matched memory control section (pins xM4 to xM1), but 8-bit and 16-bit sections remain

the same. The 32-bit MCA slot also includes a 32-bit section (pins 59 to 89).

KNOWING THE MCA SIGNALS

Enable Synchronization (ESYNC) controls VGA signals (VSYNC, HSYNC, and BLANK)

on the motherboard. When ESYNC is true, the Vertical Synchronization (VSYNC)pulses,

Horizontal Synchronization (HSYNC) , andBlanking (BLANK) signals control the display.An independent 8-bit video data bus (P0 to P7) support 256 colors on the VGA display.

VGA timing signals are controlled by theEnable Data Clock (EDCLK) andData Clock

(DCLK) signals. TheEnable Video (EVIDEO) signal switches control of the palette bus

allowing an external video adapter to provide signals on P0 to P7. Audio (Audio) andAu-

dio Signal Ground (Audio GROUND) allow the expansion board to send tone signals to

the motherboard speaker.

There are 32 address bits (Address bit 0 to Address bit 31), 11 interrupts, and 32 data bits

(Data bit 0 to Data bit 31). TheAddress Latch (ADL) signal is true when a valid address

exists on the address lines. A Channel Check (CHCK) signal flags the motherboard

when an error is detected on the expansion board. When data on the data bus is valid, the

Command (CMD) is true. The Channel Ready Return (CHRDYRTN) signal is sent to

the motherboard when the addressed expansion board I/O channel is ready. A Channel

Reset (CHRESET) signal can be used to reset all expansion boards. The Card Setup(CDSETUP) instructs an addressed board to perform a setup. TheMemory Address En-

able 24 (MADE24) line activates address line 24. The Channel Ready (CHRDY) line that

the addressed board is idle after completing its access. WhenBurst (BURST) is true, the

system bus will execute a burst cycle.

TheData Size 16 Return (DS16RTN) andData Size 32 Return (DS32RTN) tell the

motherboard whether the board is running at a 16- or 32-bit bus width. The System Byte

736 MCA BUS OPERATIONS

Video

extension

32-bit

segment

AV1

8-bit

segment

16-bit

segment

ac

AV10 A1 A45 A48 A58 A59 A89

BV1 BV10 B1 B45 B48 B58 B59 B89

FIGURE 22-1 The various elements of an MCA bus.


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TABLE 22-1 MCA 16 BIT BUS PINOUT

SIGNAL PIN PIN SIGNAL

ESYNC BV10 AV10 VSYNC

Ground BV9 AV9 HSYNC

P5 BV8 AV8 BLANK

P4 BV7 AV7 Ground

P3 BV6 AV6 P6

Ground BV5 AV5 EDCLK

P2 BV4 AV4 DCLK

P1 BV3 AV3 Ground

P0 BV2 AV2 P7

Ground BV1 AV1 EVIDEO

Key Key Key KeyAUDIO Ground B1 A1 - CD setup

AUDIO B2 A2 MADE 24

Ground B3 A3 Ground

Oscillator (14.3MHz) B4 A4 Address bit 11

Ground B5 A5 Address bit 10

Address Bit 23 B6 A6 Address bit 9

Address bit 22 B7 A7 +5 Vdc

Address bit 21 B8 A8 Address bit 8












Address bit 12 B20 A20 - ADL

Ground B21 A21 - Preempt

- IRQ 9 B22 A22 - Burst

- IRQ 3 B23 A23 -12 Vdc

- IRQ 4 B24 A24 ARB 00

Ground B25 A25 ARB 01

- IRQ 5 B26 A26 ARB 02

- IRQ 6 B27 A27 -12 Vdc

- IRQ 7 B28 A28 ARB 03

Ground B29 A29 ARB/ - GNT

Reserved B30 A30 - TC

Reserved B31 A31 +5 Vdc


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- CHCK B32 A32 - SO

Ground B33 A33 - S1

- CMD B34 A34 M/ - I/O

CHRDYRTN B35 A35 +12 Vdc

- CD SFDBK B36 A36 CD CHRDY

Ground B37 A37 Data bit 0

Data bit 1 B38 A38 Data bit 2

Data bit 3 B39 A39 +5 Vdc



CHRESET B42 A42 Data bit 7Reserved B43 A43 Ground

Reserved B44 A44 - DS 16 RTN

Ground B45 A45 - Refresh

Key Key Key Key

Key Key Key Key






Data bit 15 B53 A53 Reserved

Ground B54 A54 - SBHE

- IRQ 10 B55 A55 - CD DS 16- IRQ 11 B56 A56 +5 Vdc

- IRQ 12 B57 A57 - IRQ 14

Ground B58 A58 - IRQ 15

Reserved B59 A59 Reserved


TABLE 22-1 MCA 16 BIT BUS PINOUT(CONTINUED)

TABLE 22-2 MCA 32 BIT BUS PINOUT


Ground BM4 AM4 Reserved

Reserved BM3 AM3 - MMC CMD- MMCR BM2 AM2 Ground

Reserved BM1 AM1 - MMC

Audio ground B1 A1 -CD setup

Audio B2 A2 MADE 24

Ground B3 A3 Ground

Oscillator (14.3 MHz) B4 A4 Address bit 11


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Address bit 16 B15 A15 +5 VdcAddress bit 15 B16 A16 Address bit 2




Address bit 12 B20 A20 - ADL

Ground B21 A21 - Preempt

- IRQ 9 B22 A22 - Burst

- IRQ 3 B23 A23 -12 Vdc

- IRQ 4 B24 A24 ARB 00

Ground B25 A25 ARB 01

- IRQ 5 B26 A26 ARB 02

- IRQ 6 B27 A27 -12 Vdc

- IRQ 7 B28 A28 ARB 03Ground B29 A29 ARB/ - GNT

Reserved B30 A30 - TC

Reserved B31 A31 +5 Vdc

- CHCK B32 A32 - SO

Ground B33 A33 - S1

- CMD B34 A34 M/ - I/O

CHRDYRTN B35 A35 +12 Vdc

- CD SFDBK B36 A36 CD CHRDY






CHRESET B42 A42 Data bit 7

Reserved B43 A43 Ground

Reserved B44 A44 - DS 16 RTN

Ground B45 A45 - Refresh

Key Key Key Key



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Key Key Key Key







Ground B54 A54 - SBHE

- IRQ 10 B55 A55 - CD DS 16

- IRQ 11 B56 A56 +5 Vdc

- IRQ 12 B57 A57 - IRQ 14

Ground B58 A58 - IRQ 15





Ground B63 A63 Reserved







Reserved B70 A70 Data bit 24






- BE 0 B76 A76 Reserved

- BE 1 B77 A77 +12 Vdc

- BE 2 B78 A78 - BE 3

Ground B79 A79 - DC 32 RTN

TR 32 B80 A80 - CD DS 32



Ground B83 A83 Address bit 27Address bit 29 B84 A84 Address bit 28


Address bit 31 B86 A86 Reserved

Ground B87 A87 Reserved





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High Enable (SBHE) signal is true when the upper 16 data bits are being used, but the

Card Data Size 16 (CDDS16) signal is true when only 16 data bits are being used. If all32 bits of data are being transferred, theCard Data Size 32 (CDDS32) signal is true.

When the main memory is being refreshed, theRefresh (REF) line is true. This allows

any dynamic memory on expansion boards to be refreshed as well. TheMemory/ I/O (M/

I/O) signal defines whether the expansion board is accessing a memory or I/O location.

Signals S0 and S1 carry the status of a MicroChannel bus.

The -Preempt (-PREEMPT) signal is true when a bus arbitration cycle begins. Arbitra-

tion signals ARB00 to ARB03 indicate (in BCD) which of the 16 possible bus masters has

won arbitration. TheArbitration/ Grant (ARB/ GNT) is high when the bus is in arbitra-

tion, and low when bus control has been granted. When a DMA transfer has finished, the

Terminal Count (TC) signal is true. Byte Enable signals 0 to 3 (BE0 to BE3) indicate

which four bytes of a 32-bit data bus are transferring data. When an external bus master is

a 32-bit device, the Translate 32 (TR32) line is true. The MMCR, MMCCMD, and

MMC lines are matched memory-control signals.

PS/2 Reference and Diagnostic DisksMicroChannel (PS/2) computers require the use of a reference (or startup) disk when-

ever configuring the system, or exchanging MCA cards in their bus slots. Each time you

add, remove, or exchange an MCA card, youll need to run the reference disk. However,

reference disks are often among the first items to be misplaced as a PC is sold or passed

from owner to owner. When servicing a PS/2 system, you might easily find yourself with-

out a reference disk. Fortunately, the reference disks for many PS/2 systems (along with

a variety of diagnostic disks) can be downloaded from the IBM FTP site. Table 22-3 high-

lights the most popular FTP download addresses. Download the file to an empty directoryon the hard drive, then decompress the file. This will usually result in several individual

files, with specific instructions for creating a reference/startup disk.

CLEARING A 55SX PASSWORD

For PS/2 55sx systems, a password will prevent the reference disk from running. Youll

need to clear the CMOS RAM (including the password). Ordinarily, you can remove the

CMOS backup battery and allow the memory to clear. But for 55sx systems, you can use

the speaker cable to clear the CMOS RAM:

s Turn off your system.

s Unplug the speaker cable from the riser card and plug it in upside down.

s Turn it back on, wait for memory to count, and listen for the beep.

s Turn the system off, and plug the speaker cable right side up again.

s The password will be cleared when you power the system up again.

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For files with a .TG0 extension, you will also need to download Telegeta utility that ex-

tracts .TG0 files: ftp://ftp.pc.ibm.com/pub/pccbbs/os2_fixes/tgsfx.com


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DEALING WITH PS/2 165 ERRORS (.ADF FILES)

When running the PS/2 reference disk, youll need to have an .ADF file for each MCA

board in the system. If you encounter a 165 error when running autoconfigure with

the reference disk, chances are that the .ADF file for one or more MCA devices in the sys-

tem is missing from the reference disk. Check with the driver software that came with the

particular MCA card (its diskette might contain the needed .ADF file).

If youve got IBM-brand MCA cards in the system, you can obtain current .ADFs

(Adapter Description Files) directly from IBM. Download the ALLFILES.TXT file from:

ftp://ftp.pc.ibm.com/pub/pccbbs/allfiles.txt and locate the .ADF file for your particular

device(s). You can then navigate the FTP site and obtain the .ADF file (usually some-

where underftp://ftp.pc.ibm.com/pub/pccbbs/).

If youre using third-party MicroChannel cards, youll need to contact each particular man-

ufacturer and download the current .ADF file from their tech support areas or FTP sites.

One very good source for .ADF files for older, non-IBM MicroChannel cards is at NCRs

Web site (http://www.ncr.com/support/pc/pcdesc/library/adfs.shtml). You should also

check Peter H. Wendts Web site (http://members.aol.com/phwimage1/mcaindex.htm)

for free software that will identify MicroChannel controllers and give you the ADF file

name. The site also has a large library of .ADF files for download.


TABLE 22-3 PS/2 REFERENCE AND DIAGNOSTIC DISK FTP ADDRESSES

PS/2 25: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/25start.tg0

PS/2 25 - 286: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/rs25286a.tg0

PS/2 30: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/30start.exe

PS/2 30 - 286: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/mod30286.exe

PS/2 35/40: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/3540st.exe

PS/2 50/50z/60: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/rf5060a.exe

PS/2 53: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/rf9553a.exe (reference disk)

PS/2 53: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/rd9553a.exe (diagnostic disk)

PS/2 55sx/65sx: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/rf5565a.exe

PS/2 56/57 - 386: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/rf855657.exe

PS/2 56/57 - 486: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/rf955657.exe

PS/2 P70 (portable): ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/rfp70a.exe

PS/2 70/80: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/rf7080a.exePS/2 P75 (portable): ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/rfp75a.exe

PS/2 76/77: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/rf7677a.exe (reference disk)

PS/2 76/77: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/rd7677a.exe (diagnostic disk)

PS/2 76/77 (I or S): ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/7677ref.exe (reference disk)

PS/2 76/77 (I or S): ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/7677diag.exe (diagnostic disk)

PS/2 85 (9585): ftp://ftp.pc.ibm.com/pub/pccbbs/pc_servers/9585rf.exe (reference disk)

PS/2 85 (9585): ftp://ftp.pc.ibm.com/pub/pccbbs/pc_servers/9585rd.exe (diagnostic disk)

PS/2 90/95 (type 1): ftp://ftp.pc.ibm.com/pub/pccbbs/pc_servers/rf90951a.exe




PS/2 90/95 (all): ftp://ftp.pc.ibm.com/pub/pccbbs/pc_servers/rd9095a.exe (diagnostic disk)


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General Bus TroubleshootingIn most cases, you will not be troubleshooting a busafter all, the bus is little more thana passive connector. However, the major signals that exist on an MCA bus can provide

you with important clues about the systems operation. The most effective bus trou-

bleshooting tool available to you is a POST board. Many POST boards are equipped with

a number of LEDs that display power status, along with important timing and control sig-

nals. If one or more of those LEDs is missing, a fault has likely occurred somewhere on

the motherboard. Although most POST boards are designed for ISA bus work, Micro2000

provides an MCA adapter for their POST-Probe.

Another point to consider is that bus connectors are mechanical devicesas a result,

they do not last forever. If you or your customer are in the habit of removing and insert-

ing boards frequently, it is likely that the metal fingers providing contact will wear and

result in unreliable connections. Similarly, inserting a board improperly (or with exces-

sive force) can break the connector. In extreme cases, even the motherboard can be dam-

aged. The first rule of board replacement is: always try removing and re-inserting the

suspect board. It is not uncommon for oxides to develop on board and slot contacts that

might eventually degrade signal quality. By removing the board and re-inserting it, you

can wipe off any oxides or dust and possible improve the connections.

The second rule of board replacement is: always try a board in another expansion slot be-

fore replacing it. This way, a faulty bus slot can be ruled out before suffering the expense

of a new board. If a bus slot is defective, a technician can do little, except:

1 Block the slot and inform the customer that it is damaged and should not be used.

2 Replace the damaged bus slot connector (a tedious and time-consuming task) and pass

the labor expense on to the customer.

3 Replace the motherboard outright (also a rather expensive option).

Further StudyThats it for Chapter 22. Be sure to review the glossary and chapter questions on the ac-

companying CD. If you have access to the Internet, take a look at some of these MCA (or

PS/2) resources (in addition to the FTP references in Table 22-3):

General Technics: http://gtweb.net/mi151.html (MicroChannel Sound Card)

IBM PS/2 Reference Disks: ftp://ftp.pc.ibm.com/pub/pccbbs/refdisks/

Indelible Blue: http://www.indelible-blue.com/ (MicroChannel add-on boards)

PS/2 Parts: http://www.can.ibm.com/parts/catalogue/indexes/ps2indx.htm

Vintage PCs: http://www.can.ibm.com/helpware/vintage.html

USENET NEWSGROUP

comp.sys.ibm.ps2.hardware

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mca bus operations

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