Pdp11 Boot proms

My 11/44

The user manual describes this for the boot command:

The manual's procedure: examine 773024, where 165XYZ means boot to console mode and 173XYZ boot to a selected device, and the remaining three octal digits map onto switch pack E28.

On my 11/44 the poked memory addresses show the following:

address	value	Meaning
17765774	041460	C0
17773000	046523	MS
17773200	042114	DL
17773400	042104	DD
17773600	161777	xxx777 means no ROM present
17773024	173052	173 -> boot to selected device; sel=052?

The auto-boot mode is controlled on the M7098 Unibus module:

Section 3.3.3.2: the UBI module has five 16-pin sockets, one CPU diagnostic ROM and four device bootstrap ROMs. S1 chooses console mode or a selected-device ROM.

S2 enables or disables the internal UBI boot logic, and S3 to S10 are bits 08:01 of the bootstrap starting address. The ROMs have to sit in sequence from BT1 to BT4.

Table 3-22, which maps each ROM location to its starting address. Socket E48 is device 1, E49 device 2, E50 device 3 and E59 device 4, with the CPU diagnostic in E58.

My machine was auto-booting from socket E48, second device (apparently a MS device).

There is also an odd switch on the M7095:

Figure 3-12: the M7095 control module also carries a bootstrap control switch, S1, where ON means boot enable.

List of boot proms

This can be found here

PROM Types and equivalents

DEC Module	Prom details	Allowed types
M9312 Console PROM	1024x4 three-state	N82S137, Am27S32, 74S573, MI-7643-5
M9312, 11/44, 11/24 boot PROM	512x4 Three-state	82S131, Am27S13, 63S241, 74LS571
M9312, 11/44, 11/24 boot PROM	256x4 Three-state	82S129

Creating a boot PROM

Getting the PROMs to burn is a bit challenging, as is getting a device to burn them.. I was very lucky to get an old PROM burner: a Stag Quasar Plus. This comes with Windows XP software that knows a lot of types and which also contains really a lot of older types.

Getting the PROMs themselves was a bit harder.. These devices are old, and not easy to get. The usual route is Ebay, and my first attempt got me 10 MH74S571 proms in two weeks, which according to the number should work. But they did not: this manufacturer Tesla) only made them read compatible, writing them uses a different mechanism than all the others. Sigh.

The next attempt was a set of AM27S13 PROMs from Spain. They arrived by snail three weeks later. That is: the envelope arrived, with a nice thank you note for the order - but without PROMs. They had forgotten to put them in the envelope, so yet another three weeks to wait.

Then I got lucky: I actually found a Dutch shop (I live in the Netherlands part-time) which sold 82S129 PROMs for a sweet price - and these finally arrived… And worked

I now have an extra boot PROM for the TU58:

CZM9BE0 M9312/1144 UBI BOOT

DIAG. ROM (E20) (FOR 11-44 UBI: E58)C0

BOOTSTRAP ROM ENTRY POINTS AND DEVICE CODES
LOC.             NO DIAG.       RUN DIAG.       DEVICE CODE

ROM 1(E48)      173004          173006          MS
ROM 2(E49)      173204          173206          DL
ROM 3(E50)      173404          173406          DD

PSEUDO POWER-FAIL VECTOR ADR./NEW PC    173024  173052
ROM SEQUENCE IS INCORRECT AS PER INSTALLATION PROCEDURE.

SEQUENCE SHOULD BE:

ROM 1(E48)      DD
ROM 2(E49)      DL
ROM 3(E50)      MS

Links:

Jorg Hoppe’s site