M9301 ROM
The M9301 ROM card was a UNIBUS ROM card for the PDP-11 series of computers. It contained 512 words of memory, all readable directly from the UNIBUS (i.e. not windowed). A DIP switch bank provided configuration. The M9301 also provided termination for the UNIBUS.
It was a dual format card, intended for use in the two top (AB) connectors of a MUD slot, or in a UNIBUS in/out slot.
Most versions were used for bootstrapping the machine, from disk, paper tape, magnetic tape, etc, but it could be use for any purpose; most DEC-supplied pre-programmed versions included a console emulator, and basic diagnostics. A command to boot the machine could be given in the emulator, using a symbolic device code.
It used four 4-bit wide PROMs to hold the data. The board occupied addresses 773000-773776 and 765000-765776; a configuration switch allowed the lower block to be disabled.
Other configuration switches controlled which address the CPU jumped to on power on (a clever kludge, controlled by another configuration switch, allowed the board to force the CPU to read its power-on PC and PS from the ROM, at a location set by still other configuration switches, thereby allowing auto-boot on power-on).
The board came in several main variants, designated M9301-Yx (where 'x' is a capital letter, starting with 'A') came pre-programmed from DEC to perform various functions.
There were two different etch revisions of the card itself, but they seem to be programming-wise identical.
Contents
Configuration switches
The board contains a single 10-switch DIP switch, S1, which controls the board's behaviour.
If S1-1 is set to 'off' (open), the low bank of memory on the card (765000-765777) is disabled; when 'on' (closed) it is enabled.
If S1-2 is 'off', the system will power-up normally; if 'on', the CPU will obtain its new PC/PS pair from locations 173024 on the card, which contain a mixture of bits from the ROM (high bits) and the configuration switch (low bits), which can be used to force the CPU to start executing in the ROM on power-on. (This is done by asserting the appropriate high address lines on the UNIBUS for the first two bus cycles after power-up; a technique pioneered by the BM873 ROM.)
Switches S1-3 through S1-10 contain bits 8 through 1 of the power-on PC (above); the exact meaning will depend on the board variant (below).
Connector tabs
The board contains three connector tabs, which may be used with external switches, to control the board's behaviour.
One, TP3, is a ground return. TP2, when momemtarily grounded, forces the machine to execute a power-fail/restart sequence (by asserting UNIBUS line ACLO). TP1, when grounded, forces the machine to execute the on-board ROM on power on, no matter what the position of S1-2 (above).
Variants
- M9301-YA - (ROMs 034A9, 035A9, 036A9, 037A9) - PDP-11/04 and PDP-11/34 OEM version; had basic diagnostics, console emulator, booted from various devices (RK11 and RP11 disks, TC11 DECtape, TM11 magnetic tape, serial line, PC11 high-speed paper-tape reader, TA11 casette tape, RX11 8-inch floppy disk), supported auto-boot on power on, and also power-fail restart
- M9301-YB - (ROMs 038A9, 039A9, 040A9, 041A9) - /04 and /34 end user version; had basic diagnostics, console emulator, booted from various devices (RK11, RP11, TC11, TM11, TA11, RX11, serial line, high-speed paper-tape reader, RJS, RJP, TJU), also power-fail restart
- M9301-YC - PDP-11/70 version; contained basic CPU, cache and memory diagnostics, booted from various devices (TM11, TC11, RK11, RP11, RK611, RJS, RJP, TJU, RX11)
- M9301-YD - All models; contained code to allow a terminal attached to the machine to be a terminal on some other line; also had boot code for RX11 and DDCMP
- M9301-YE - All models; had basic diagnostics, console emulator; booted from low speed paper tape or DECnet; supported auto-boot on power on, and also power-fail restart
- M9301-YF - (ROMs 480A9, 481A9, 482A9, 483A9) - All models (auto-start not available on PDP-11/45, PDP-11/50); had basic diagnostics, console emulator, booted from various devices (RK11, RK06, RP11, TC11, TM11, TA11, RX11, serial line, high-speed paper-tape reader, RJS, RJP, TJU), supported auto-boot on power on, and also power-fail restart
- M9301-YH - (ROMs 332A9, 333A9, 334A9, 335A9) - /60 and /70 version; contained basic CPU, cache and memory diagnostics, booted from various devices (TM11, TC11, RK11, RP11, RK06, RJS, RJP, TJU, RX11, high-speed paper-tape reader)
- M9301-YJ - All models; had basic diagnostics, console emulator; booted from DECnet, and various devices (RX11, TU, serial line, DMC), also power-fail restart
Entry points
DEC ROM programs can be started manually, on machines with a front panel which allow that. Useful entry points (all in octal) are given here.
M9301-YA
| Location | Function |
|---|---|
| 173000 | Console emulator w/ CPU Diagnostics |
| 173002 | Diagnostics, then emulate power-fail restart trap through 24 |
| 173030 | Console emulator (no diagnostics) |
| 173440 | RK11 Boot w/ Diagnostics |
| 173442 | RK11 Boot (no diagnostics) |
| 173466 | RP11 Boot w/ Diagnostics |
| 173470 | RP11 Boot (no diagnostics) |
| 173506 | TC11 Boot w/ Diagnostics |
| 173570 | TC11 Boot (no diagnostics) |
| 173524 | TM11 Boot w/ Diagnostics |
| 173526 | TM11 Boot (no diagnostics) |
| 173624 | TA11 Boot w/ Diagnostics |
| 173626 | TA11 Boot (no diagnostics) |
| 173636 | RX11 Boot w/ Diagnostics |
| 173640 | RX11 Boot (no diagnostics) |
| 173650 | DL11 Boot w/ Diagnostics |
| 173652 | DL11 Boot (no diagnostics) |
| 173660 | PC11 Boot w/ Diagnostics |
| 173662 | PC11 Boot (no diagnostics) |
Note that switch S1-1 must be on for all the choices with diagnostics.
M9301-YB
| Location | Function |
|---|---|
| 173000 | Console emulator w/ CPU Diagnostics |
| 173002 | Diagnostics, then emulate power-fail restart trap through 24 |
| 173226 | Console emulator (no diagnostics) |
M9301-YF
| Location | Function |
|---|---|
| 165404/173000* | Console emulator w/ CPU Diagnostics |
| 165406/173002* | Console emulator (no diagnostics) |
| 173040 | RP11 Boot w/ Diagnostics |
| 173042 | RP11 Boot (no diagnostics) |
| 173054 | TU16 Boot w/ Diagnostics |
| 173056 | TU16 Boot (no diagnostics) |
| 173144 | RK11 Boot w/ Diagnostics |
| 173146 | RK11 Boot (no diagnostics) |
| 173174 | TC11 Boot w/ Diagnostics |
| 173176 | TC11 Boot (no diagnostics) |
| 173224 | RP04/5/6 w/ Diagnostics |
| 173226 | RP04/5/6 Boot (no diagnostics) |
| 173364 | DL11 Boot w/ Diagnostics |
| 173366 | DL11 Boot (no diagnostics) |
| 173440 | RS03/4 Boot w/ Diagnostics |
| 173442 | RS03/4 Boot (no diagnostics) |
| 173474 | TM11 Boot w/ Diagnostics |
| 173476 | TM11 Boot (no diagnostics) |
| 173544 | RX11 Boot w/ Diagnostics |
| 173546 | RX11 Boot (no diagnostics) |
| 173644 | Diagnostics, then emulate power-fail restart trap through 24 |
| 173646 | Emulate power-fail restart trap through 24 |
| 173662 | RK611 Boot w/ Diagnostics |
| 173664 | RK611 Boot (no diagnostics) |
| 173704 | PC11 Boot w/ Diagnostics |
| 173706 | PC11 Boot (no diagnostics) |
Note that switch S1-1 must be on for all the choices with diagnostics, and also the console emulation and power-fail restart choices.
* - The manual gives the 16540x locations for manual start locations, but the configuration DIP switch settings correspond to the 17300x locations.
See also
External links
- M9301 bootstrap/terminator module maintenance and operator's manual (EK-M9301-TM-001)
- UNIBUS Terminator/Bootstrap Engineering Drawings
- Disassembled and commented M9301-YA ROM code
- Disassembled and partially commented M9301-YB ROM code
- Disassembled and partially commented M9301-YF ROM code
- Disassembled but mostly un-commented M9301-YH ROM code
