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ZXnet http server: Digital MicroVAX 3500



DEC Systems

DEC hardware
Digital Equipment Corporation logo

Quick Specs
Architecture: CVAX
CPU: KA650 (22MHz)
Max Ram: 64MB ECC
chassis: pedestal
bus: QBus

Digital MicroVAX 3500

The MicroVAX 3500 was introduced in 1987 along with the MicroVAX 3600 as the higher end complement of the MicroVAX family. The new machines featured more than three times the performance and twice the memory capacity of the MicroVAX II.
MicroVAX 3500

The MicroVAX 3500 (essentially the same as the VAXserver 3500) comes in a BA213 chassis which contains a 12-slot backplane wired Q/CD. This means that QBus runs over the top two connectors and the bottom two are the C/D interconnect. QBus cards must be installed using the top two connectors - cards installed in the bottom two wont function.

The machine comes standard with a TQK70 TMSCP controller, a TK70 drive and the 22MHz KA650 CPU which lives in slot 1. One to four MS650 memory boards are supported in slots 2 through 5.

CPU Cover Panel Controls

[CPU Switches & Controls on CPU Cover Panel from EK-O30AB-IS-002]

The image to the left shows the controls on the CPU Cover panel (from EK-O30AB-IS page 1-4). It contains the break enable/disable switch, powerup mode switch, LED Display, and a Modified Modular Jack for the console terminal.

Break Enable/Disable Switch
Switch Position Function
Dot outside circle (down) [Dot In Circle]   Break disable (factory setting). With the switch in this position, pressing the break key has no effect on the system. On powerup or after a reset, the system attempts to boot the operating system
Dot inside circle (up) [Dot inside circle]   Break enable. With the switch in this position, pressing the break key on the terminal halts the CPU. Additionally, after powerup or after a reset the system will go into console I/O mode after the self-tests have completed.
Powerup Mode Switch
Switch Position Mode
Human Profile [Human Profile]    Language inquiry. If the terminal supports multinational character sets, the user is prompted for language on every powerup and after a reset. Full startup diagnostics are run.
Arrow [Arrow]   Run (factory setting). The user is only prompted for language on powerup and after reset if the battery backup unit has failed. Full startup diagnostics are run.
T in a circle [T in a circle]   Test mode. ROM programs run wraparound serial line unit tests. A loopback connector is required.
LED Display

The LED display shows the powerup tests. If you power up a VAX with no console attached and the screen counts down to 3 then the machine is probably OK. It counts down to 0 when it has booted.

F: Waiting for CDOK
E: Start executing ROM firmware code
D: Waiting for Power OK
C: SSC and ROM tests
B: CPU tests
A: FPA tests
9: Memory management chip tests
8: Memory tests
7: Qbus tests
6: Console loopback/QDSS tests
5: Cache tests
4: Misc. tests running
3: Console I/O mode
2: Searching for bootstrap device, control passed to VMB
1: Bootstrap device found, control passed to secondary bootstrap
0: Program I/O mode, control passed to operating systems

Battery Backup Unit

[leaking battery backup unit]

Behind the CPU cover panel is a battery backup unit (part number 12-9245-01) made of 3* 1.2V NiCd cells wired in series. The purpose of this battery is to keep the correct time of year and the CPUs language settings when the system is switched off.

After a time, this battery may begin to leak (pictured left, click for larger image). The BBU in my first MicroVAX 3500 has made quite a big mess behind the CPU cover panel. The one on my second MicroVAX 3500 appears to have failed but has not yet started leaking. I have removed both to prevent any further or future damage.

The system runs just fine with the battery removed. The only problem is that it wont remember the time, language selection, etc.


I currently own two MicroVAX 3500s, both from DSIR:
akvax - my first ever VAX
lhnvax - my second MicroVAX 3500 which I got at the same time as a VAXstation 4000/60.


Images of akvax are available here. Images for lhnvax are available here.


See also