PDP 11/73 is ALIVE!

From: der Mouse <mouse_at_Rodents.Montreal.QC.CA>
Date: Sun Nov 23 14:26:38 2003

>> Powering it up gives me the _at_ prompt.
> This is the ODT Prompt. Unfortunately I have never found a good
> documentation about ODT commands. Maybe someone else can help with
> this?

Here are the notes I took back when I had a physical KDJ11-A manual to
refer to:

Powerup sequence:

        Turn off LED 1
        Assert BINIT L
        Wait 10 uS
        Negate BINIT L
        Clear MMR0
        Clear MMR3
        Wait 90 uS
        Clear PIRQ
        Clear FPS
        do {
                Read jumpers
                Clear CPU ERROR
        } while BPOK H is negated
        Set CCR<8> to flush cache, and clear all other CCR bits
        Clear MSER
        Clear PS
        Set CPU ERROR to 0177766
        Read CPU ERROR
        Clear CPU ERROR
        if (value read equals value written) turn off LED 3
        Read memory location 0
        if (no NXM abort) {
                Read memory location 0177700
                if (NXM abort) {
                        Turn off LED 2
                }
        }
        Read memory location 177560
        if (no NXM abort) turn off LED 4
        switch (powerup option) {
                case 0: pc_at_24, ps_at_26, begin execution
                case 1: ps=0, enter ODT
                case 2: pc=173000, ps=340, begin execution
                case 3: pc=(user boot << 12), ps=340, begin execution
        }

ODT G command:
        Turn off LED 4
        Assert BINIT L
        Wait 10 uS
        Negate BINIT L
        Clear MMR0
        Clear MMR3
        Wait 90 uS
        Clear PIRQ
        Clear FPS
        do {
                Read jumpers
                Clear CPU ERROR
        } while BPOK H is negated
        Set CCR<8>
        Clear MSER
        Clear PS
        Begin execution

ODT entry:
        DATI from RBUF (017777562) and ignore the character.
        Print <CR> <LF>
        Print R7 in %06o
        Print <CR> <LF>
        Print _at_
        Enter wait loop

ODT input sequence:
        Busy-wait using DATI for RCSR (017777560) bit <7> to become 1
        DATI from RBUF (017777562) and use low byte

ODT output sequence:
        Busy-wait using DATI for XCSR (017777564) bit <7> to become 1
        DATO to XBUF (017777566) with character in low byte; high byte is undefined

If XCSR bit <6> (interrupt enable) is set, program will get interrupt when P command is used.
If G is used, BINIT L is supposed to clear all interrupt conditions.

ODT has 10 internal states. Each echoes unknown characters as ? and ignores them.
ODT echoes parity bits faithfully but ignores them when processing. Generated characters have 0 parity.
All commands are echoed except for <LF>.
R6 is the stack pointer selected by the PS.
The PS responds to bus address 17777776; R0-R7 are not accessible by bus addresses.
MMU registers are accessible by their bus addresses.
Bus timeout generates "?\r\n_at_".

ODT commands:
        / Open a bus address or processor register.
                _at_R3/123456 open R3
                _at_RS/123456 open PS
                _at_1000/123456 open location 01000
                With no specifier,
                _at_/123456 re-opens just-modified location
                                (if none, ie if just entered ODT, ? is given.)

        <CR> Close open location. If new data precedes the <CR>, thing is changed.
                Reponse: <CR> <LF> _at_

        <LF> Close open location, open next location. (If PS is open, this is like <CR>.)
                Doing this when R7 is open gets to R0.
                Address rollover is modulo 32K; to cross a 32K boundary, the address must be re-entered.
                Is echoed unusually; response is <CR> <LF> _at_, then sequence to open next location.

\0, \2, \12 are echoed as "?\r\n_at_".

        $ is alternative to R for register designation with / command. If more than one character follows
        R (or $), last one is used, unless last three are 077 or 477, in which case PS is used.

        The T-bit of the PS cannot be changed by ODT (misfeature?).

        G Go. Echoed, then \0\0 is printed to flush the G, then above sequence is executed.

        P Proceed. No programmer-visible state is altered. After the P is echoed, the machine
                is in instruction-fetch microstate.

        ^S Binary dump. After the echo, two 8-bit bytes are expected, high byte first; they are not
                echoed. These form a starting address in the first 64K of core. ODT responds by dumping
                8 bytes from that address in raw binary, then <CR> <LF> _at_.

        H Reserved to DEC in the future. Treated as an invalid character.

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Received on Sun Nov 23 2003 - 14:26:38 GMT