On a Sun Ultra 10 system board, there is a plain 32-pin header next to the PCI riser connector that the documentation describes as ROMBO. What is that? What would connect here?

Other than the table for JP1, which allows selecting ROMBO instead of FPROM, there is no further reference to ROMBO in the Ultra 10 documentation I can find. Assorted other sun-4 platforms have a similar connector, but I can't find any explanation of its use.

a picture of one corner of a Sun Ultra 10 mainboard, with the "ROMBO"

  • And if I'd have to guess: ROMBO = ROM-Break-Out?
    – dirkt
    Jun 27, 2018 at 19:05
  • @dirkt That was my initial thought too but the pinouts suggest something a bit more complex. More on that later... Jun 27, 2018 at 21:36

2 Answers 2


It appears to have been used for some kind of factory testing. It seems to hook into the PROM bus so it's likely to allow reprogramming of the boot PROM, a socket for a ROM emulator, or to allow easy connection of an alternate (diagnostic) ROM. The presence of a chip select line makes me suspect it's the latter. The documentation I've seen is not really clear on this and it's possible that different versions had different functionality. It's probably not for general QA or the like since the boards also have JTAG headers.

I don't have a 32-pin pinout but here are a couple of variants that should give you an idea of how they functioned.

28-pin (SROMBOlite):

        +5V 1    2 GND
    EB_RD_L 3    4 EB_WR_L
   EB_RDY_L 7    8 EB_DAT0
    EB_DAT1 9   10 EB_DAT2
    EB_DAT3 11  12 BRST_L
    EB_DAT4 13  14 EB_DAT5
    EB_DAT6 15  16 EB_DAT7
 ROMBO_CS_L 17  18 EB_ADR0
    EB_ADR1 19  20 EB_ADR2
    EB_ADR3 21  22 SYNC_SER_IRQ_L
    EB_ADR4 23  24 EB_ADR5
    EB_ADR6 25  26 EB_ADR7
        +5V 27  28 GND

and the 34-pin SROMBO variant:

ADR19 1   2 VCC
ADR16 3   4 ADR18
ADR15 5   6 ADR17
ADR12 7   8 ADR14
 ADR7 9  10 ADR13
ADR6 11  12 ADR8
ADR5 13  14 ADR9
ADR4 15  16 ADR11
ADR3 17  18 RD_L
ADR2 19  20 ADR10
ADR1 21  22 ROMBO_CS_L
ADR0 23  24 DAT7
DAT0 25  26 DAT6
DAT1 27  28 DAT5
DAT2 29  30 DAT4
 GND 31  32 DAT3
  NC 33  34 WR_L

It's a replacement for the FPROM (Flash PROM) which is the firmware that performs a power-on-self-test (POST) and then boots the operating system. The ROMBO appears to be used by Sun during the development of the firmware, at least according to Sun Blade 150 Service Manual:

There is a ROMBO connector for OpenBoot PROM and POST software development during initial bringup phase

  • I came across the remark in the Blade 150 service manual also, but it didn't occur to me at the time that "initial bringup phase" meant something other than booting, but of course to a computer engineer I guess it means firmware development with early board production runs or maybe a bit earlier still with custom prototypes
    – rakslice
    Jul 2, 2018 at 3:40

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