The Rough Guide to MBus Modules
Introduction Buses Modules Systems Chips Miscellany

SPARCstation-20


System

The SS20 system bus is a 40/50 MHz MBus with 2 slots for plug-in MBus modules.

Configurations using a single module must locate that module in slot 0 (the lower one).


Firmware Versions

Older systems may require BootPROM upgrades to be able to use newer MBus modules. Where known, the minimum BootPROM level is listed in the module configuration table.

The last available BootPROM is version 2.25 from Sun, or 2.25R from Ross/Bridgepoint.

WARNING:
The 2.25 and 2.25R PROMs have real behavioural differences.

The Ross 2.25R PROM enables RT620D-based HyperSPARC modules. The Sun 2.25 PROM does not.

The Sun 2.25 PROM works with SM52, at least some SM52X, and (at least in part) with SM51-2, SM61-2, SM81-2 and pairs of some SM40 modules. The Ross 2.25R PROM might not.

There may be other differences.

The Ross 2.25R PROM can often be distinguished by the word "splug" on the label.


Overheating

The SS20 enclosure is better ventilated than the SPARCstation-10. The SS20 motherboard is intrinsically more resistant to ambient temperature problems caused by hot MBus modules. It also has a larger-capacity DC power-supply unit. Thus the SS20 is much less prone to overheating than the SS10.

However, some configurations are still considered risky.

Configurations rated as deadly should not be used without additional cooling, ie: external fans to push more and cooler air into the PSU intake at the right-hand side of the chassis (when viewed from the front).

Configurations rated as very hot should not be used in fully-populated systems (ie: no free SBus slots, and more than four DSIMMs/VSIMMs) without great care, or at least some additional cooling.

Also, the ZX and TurboZX (Leo) SBus graphics cards generate a huge amount of heat; the TurboZX draws a mind-boggling amount of power from four (yes, power from all four) SBus slots. If you have a ZX or TurboZX card installed, you should avoid configurations rated very hot; in the case of TurboZX, you should also avoid configurations rated merely fairly hot.

Similar precautions might be prudent if you have a Fujitsu AG-10 graphics card installed.

Prolonged disregard for the above guidelines is likely to result in damage:

NOTE:
The heat-ratings are normalised against an ambient air temperature of upto 30 Celcius. If the external air temperature is above 30 Celcius, you should take extra care.


System Jumper Settings

The SS20 motherboard has two different jumper settings for MBus speed:

MBus Clock Jumpers
Automatically selected 40MHz or 50MHz
(factory setting)
J1401: jumper on pins 2-3
Fixed at 40 MHz J1401: jumper on pins 1-2

NOTE: the SS20 clock-speed jumper should be in the factory-preset (auto-select) position, except where noted in the module configuration table.


Other Issues

The SS20 has two rows of two SBus slots for peripheral expansion (SCSI cards, framebuffers, serial-port cards, etc). Each double-width MBus module blocks an SBus slot on a different row, reducing the maximum number of single-width and double-width SBus cards by one. Thus an SS20 with two double-width MBus modules would have only 2 single-width SBus slots available.

Inserting cards into (or extracting from) the top MBus slot requires temporary removal of any DSIMM or VSIMM in slot 4 for the duration of the insertion (or extraction) procedure.


MBus Module Configuration Table

Specific part-numbers are only listed where significant.

See also: General Module Configuration Rules, which also covers mixed-module configurations.

Note: some configurations have particular caveats, such as failing to provide the level of performance that one might intuitively expect, or dangerous overheating, and so on. Such configurations are marked with a footnote-number in square brackets.

Module Type No. of
(identical)
Modules
Functional? Min. PROM level
CYM6001K 1 yes [10] 2.12
2 no n/a
SM100 1 yes [11] 2.12
2
SM20
SM21
SM30
1 no n/a
2
SM40
501-2219
501-2295
1 yes  [1] 2.12
2 no n/a
SM40
501-2358
501-2570
1 yes  [1] 2.12
2 2.14
SM41
(33MHz)
501-2318
1 no n/a
2
SM41
501-1714
501-2258
501-2270
501-2359
1 yes 2.12
2
SM52 1 yes  [2]  [8] 2.12?
2 yes  [2]  [9]
SM52X
501-2431
1 probably  [2] 2.12
2
SM52X
501-2609
1 yes  [3] 2.12
2
SM52X
501-2756
501-2780
1 yes  [1] 2.12
2
SM520 1 yes 2.12  [6]   or 2.25
2
SM521 1 no n/a
2
SM50 1 yes 2.12
2
SM51
501-2352
501-2360
501-2361
501-2387
1 probably  [2] 2.12
2
SM51
501-2562
1 yes  [4] 2.12
2
SM51
501-2607
501-2617
501-2707
501-2754
1 yes  [1] 2.12
2
SM61
501-2571
1 yes  [2] 2.12
2
SM61
501-2519
501-2613
501-2752
501-2769
501-2782
501-2825
1 yes 2.12
2
SM51-2 1 yes  [1]  [5] 2.12
2
SM61-2 1 yes  [5] 2.12
2
SM71 1 yes 2.22
2 yes  [7]
SM81 1 yes 2.22
2 yes  [8]
SM81-2
SM91-2
1 yes  [5] 2.22
2 yes  [5]  [8]
HMx1S-256 1 no n/a
2
HM55any-256
HM66any-256
1 yes  [2] 2.19
2
HM72any-256
HM80S-256
HM90any-256
HM100any-256
HM110D-256
HM125any-256
1 yes 2.19
2
HM110any-1024
HM125any-512
HM125any-1024
HM133any-512
HM142S-1024
1 yes 2.25 and 2.25R
2
HM142W-1024
HM150S-512
HM166S-512
1 yes 2.25 and 2.25R
2 yes  [7]
HM150D-512 1 yes 2.25 and 2.25R
2 yes  [8]
HM150W-512 1 yes (2.25 and 2.25R)
2 yes  [7]
HM180S-512
HM180D-512
1 yes 2.25R
2
HMx4.5S-512 1 yes  [3] 2.25R
2
HMx4S-512
HMx4D-512
1 yes 2.25R
2

Footnotes:
1.
Automatically limits the MBus to only 40MHz.
2.
May require the MBus speed to be limited to 40MHz - see system jumper settings.
3
Requires the MBus speed to be limited to 40MHz - see system jumper settings.
4.
The Sun Field Engineers handbook states quite strongly that revision -01 of these modules should not be used in the SPARCstation-20. It is not clear why (it cannot be for heat or current-drain reasons as they are intended for the SPARCstation-10). It may be because they do not properly support the MBus speed-selection protocol of the SPARCstation-20. If so, the revision -01 modules will work fine, as long as the MBus speed is limited to 40MHz - see system jumper settings.
5.
Only 1Mb of the 2Mb per-module cache memory is used.
6.
The SM520 might behave as a single-CPU module if the SS20 is fitted with a PROM revision less than 2.25.
7.
Fairly hot. Generally OK, but see Overheating.
8.
Very hot. Safe enough if caution taken. See Overheating.
9.
Deadly. See Overheating.
10.
If the system jumpers are set to limit the MBus speed to 40MHz, the CYM6001K module works in the SS20 at the hardware and MBus level; however Solaris 2.4 and later releases do not quite work on such a configuration. Earlier Solaris releases, or SunOS 4.x, may behave differently.
11.
If the system jumpers are set to limit the MBus speed to 40MHz, SM100 is fully functional (both CPUs active) in the SS20 under SMP-capable versions of NetBSD; however it is unknown how SunOS 4.x or Solaris behave on such a configuration: I would expect that both SunOS 4.1.3_U1 edition B or later, and Solaris 2.3 edition II or later, can be used, but this has not yet been confirmed. See also footnotes 2 and 3 of the Cypress-SPARC MBus Modules table.

Introduction Buses Modules Systems Chips Miscellany
Mike Spooner, revised 16th June 2004