A PDP-11 Monitor This monitor is for the S100 bus PDP-11 CPU board described
here.
Unlike the Intel family of CPU's, the PDP-11 starts up using a "Power On
Circuit" that either directs the CPU to its own internal (simple) monitor
or to and external ROM. This is all described in some detail
here.
Here is how the monitor signs on when the CPU gets control of the S100 bus with
the Z80 Monitor "O" command.
Please note this monitor is currently under active development (April 2018). There are
sections that call upon the "PDP-11 Support" board to load an OS from a TU58
tape drive that are not complete. Please return here from time to
time for updated versions. Here is a list of the main functions within the PDP-11 monitor I have written so far:-
Setup all equates for ports and memory locations etc.
From the A-Z command jump table go to:-
Display memory map for 0 to FFFFH
XModem -- File downloads
Display RAM
Echo a keyboard character on console
Fill RAM with a HEX value (Bytes)
GoTo a RAM location
Fill RAM with a HEX value (Words)
Display the bit pattern of the IOBYTE port
Display menu on console
Rapid port ASCII output test to console
Move and verify memory
Query and set ports with Bytes or Words
Setup Interrupt vector table in RAM and activate all interrupts
Substitute values in RAM (Bytes)
Display ASCII in RAM
Test
Speech output routine
Verify two RAM areas are the same
Tu58 Tape Drive Sub-Menu
Test Event timer
Turn off Interrupts
Switch back to Z80 CPU
Support routines Table of pointers to routines within the monitor
Data area
Also please note there are various equates at the start of the monitor code
that you need to adjust depending on your need (S100_ONLY,for example).
V2 PDP11 Monitor.
The V1.5 monitor almost completely fills the C000H to
DFFFH available space on
both the "V1"
and
V2
PDP11 CPU Boards. On the V2 CPU board if we jumper K12 to 2-3 we
can utilize pin 2 of the 28C64 EEPROMs to select the upper or lower "half" of the
EEPROM as defined by its A12 address line. Code in the U25 CPLD allows us
to make this selection by inputting from the S100 bus ports
00E4H or 00E5H.
While this complicates the Monitor code it allows one to almost double the
amount of code you can get into a 4K address space. All versions of the PDP11
Monitor from V2.0 onwards have this capability/code. The most current
version can be download from below. Programming these two EEPROMS is
a bit tricky however. First here is a diagram of the layout:
The actual PDP monitor assembly language code is split into two completely
separate files, PDP_MON_LOW_PAGE.MAC and
PDP_MON_HIGH_PAGE.MAC. It is very important to
understand that the code in either file knows nothing about the code in the
other. The vast majority of the monitor code (currently) resides in the
PDP_MON_LOW.MAC file. In fact you can use this
code/file alone to run the monitor just as you did for the earlier "single page"
monitor e.g. the V1.5 monitor. It will for example run fine in the original
V1.1 PDP11
CPU board. Currently two menu options, The "C" (XModem) and "O" (IO Ports)
commands reside in the High Page for the V2 and later versions. Any further new code will probably also
reside there.
How do we switch the Address Line LA13 on the ROM without blowing the running
CPU out of the water? We do this by having a small "Switch Address
Line" routine in exactly the same location in both the LOW and
HIGH ROM code sections.
In both files (and so pages of the ROM) the beginning code is:-
LOW PAGE ROM:- Start: MOV #CPU_STACK,SP
; LOW ROM & HIGH PAGEs: Setup stack at BF00H (Below ROM ORG at C000H)
MOV #&00E0,@#PSW
; Block ALL Interrupts (Clear bits 7-5)
JMP SKIP
; Skip to the hardware initialization/running
Align
ACTIVATE_HIGH_PAGE:
; SWITCH TO HIGH PAGE ROM MOVB @#ROM_HIGH_PORT,R1
; Switch the LA13 Address line input to the ROMs HIGH. MUST be to an even byte
JMP NoHighPageError
; Will arrive here only IF no address line LA13 switch. Must be inactive (Check
JP K12)
Align
ACTIVATE_LOW_PAGE:
; RETURN BACK TO LOW PAGE ROM NOP
NOP
JMP Loop1
; <---- Switching back to LOW page will arrive here
SKIP:
______________________________________________________________________________________________________________ HIGH PAGE ROM:- Start: MOV #CPU_STACK,SP
; LOW ROM & HIGH PAGEs: Setup stack at BF00H (Below ROM ORG at C000H)
MOV #&00E0,@#PSW
; Block ALL Interrupts (Clear bits 7-5)
JMP NoLowPageError
Align
ACTIVATE_HIGH_PAGE:
; <---- ARRIVE HERE FROM LOW PAGE NOP
NOP
JMP HIGH_Loop
Align
ACTIVATE_LOW_PAGE:
; <----- JUMP BACK TO LOW PAGE MOVB @#ROM_LOW_PORT,R1
; Switch the LA13 Address line input to the ROMs LOW. MUST be to an even byte
JMP NoLowPageError
; Will arrive here only IF no address line LA13 switch. Must be inactive (Check
JP K12)
NoLowPageError:
The trick is that when we input (anything) from the port
ROM_HIGH_PORT the code in the U25 CPLD
recognizes this event and switches the address line LA13 from LOW to HIGH going
to both EEPROMS. The yellow text code
above moves (unknown to the CPU) from the lower to the upper ROM page. This
common code is the link between both pages. We load a menu option number
into the R3 register, jump to the "Switching Routine", it is picked up in the
HIGH page and processed in the normal way depending on the R3 menu number passed
to it.
When done, we jump to the ACTIVETE_LOW PAGE which lowers the LA13 line and
again, unknown to the CPU it ends up in the LOW PAGE. This code is
in purple above.
It takes a little time to really understand this process. Remember the CPU
does not know anything about this process. After the port input is done
the CPU does whatever the next opcode in that ROM (page) requires.
This facility allows us plenty of future space to write quite elaborate
functions in the 4K (now 8K) ROM space between C000H
and DFFFH on the V2 CPU board. Within the PDP11 Monitor.zip file I also provide a "PDPL.bat" and
"PDPH.bat" to automate the assembly process under windows.
There is however one catch, programming the ROMs is quite tricky.
You have to place the 4 segments of code exactly as shown in the above diagram.
It would be easier if our assembler generate .HEX
code but it only generates .bin files.
You are already familiar by now I assume of burning the .bin file
EVEN and ODD
bytes into two ROMS. The added twist here is we need to place two
files in the EVEN bytes ROM and two files in
the ODD bytes ROM. You have to be careful
when you load up the second file you don't overwrite the first file.
Different PROM Burners probably have different ways of doing this. Here is the
process for a Wellon VP-290 (or VP299)
with 28C64's EEPROMS :-
Assemble and make two .bin files, PLP_MON_LOW_PAGE.bin and
PDP_MON_HIGH_PAGE.bin.
Be sure you configure the equates at the start of
both files correctly before assembly. In particular make sure you have:
ROM: equ TRUE
For the EVEN bytes ROM:-
Load the Wellon programmer program.
From the Edit menu
Fill the buffer with 00's and close it.
Load the file PDP_MON_LOW_PAGE.bin with the
following settings:
For File Mode use "Even" and Clear Buffer Options
= Disable
Leave the "File Address(Hex) as 0000 and the "To Buffer
Address (HEX) as 0000H)
For "Auto Format Detect" use bin
Leave the File size (for a 28C64) to 2000H
Load the file PDP_MON_HIGH_PAGE.bin with the
following settings:
For File Mode use "Even" and Clear Buffer Options
= Disable
Set the "To Buffer
Address (HEX) as 1000 and the"File Address(Hex) as
0000)
For "Auto Format Detect" use bin
Set the File size (for a 28C64) to
1000H
Program ("Burn" ) the above ROM code.
When done, read the data back with the Read
button. Then open the Edit buffer and
scroll down the 100H sections. You should see the following:-
Repeat for the ODD bytes ROM:-
From the Edit menu
Fill the buffer with 00's and close it.
Load the file PDP_MON_LOW_PAGE.bin with the
following settings:
For File Mode use "Odd" and Clear Buffer Options
= Disable
Leave the "File Address(Hex) as 0000 and the "To Buffer
Address (HEX) as 0000H)
For "Auto Format Detect" use bin
Set the File size (for a 28C64) to 2000H
Load the file PDP_MON_HIGH_PAGE.bin with the
following settings:
For File Mode use "Odd" and Clear Buffer Options
= Disable
Set the "To Buffer
Address (HEX) as 1000 and the"File Address(Hex) as
0000)
For "Auto Format Detect" use bin
Set the File size (for a 28C64) to
1000H
Program ("Burn" ) the above ROM code.
When done, read the data back with the Read
button. Then open the Edit buffer and
scroll down the 100H sections. You should see the following:-
With this dual page feature you have an extended list of Monitor options. The
HIGH PAGE options currently are the "C" and "O"
commands. They have square brackets around them in the menu, but otherwise
behave exactly like the other menu items. Obviously if you are using
the V1.1 Board or only burn in the LOW ROM PAGE they will not be available.
The monitor code will detect this and warn you.
Here is what the monitor signon looks like for a few commands.
As you can see programming both EEROMS is quite tricky. Some ROM programmers may
not in fact let you do a reburn as described above. When you are first
building your board (or for the V1 board) just use the
PDP_ROM_LOW_PAGE file
and use do a simple "normal" Odd/Even ROM burn. Remember you do not need
the HIGH page mode to boot up the monitor.
Please remember this PDP11 Monitor contains a few critical equates at
he start of both the HIGH and LOW Page listings. Take care to set then exactly
to suite your needs. ROMS: equ TRUE
; <<<<< Set to FALSE for test program running at 1000H in RAM (10000 Octal)
>>>>>
DETAILED_INTS: equ TRUE
; Set to TRUE for detailed UART Interrupt data display. (Note characters must be
entered slowly)
ST8C4: equ FALSE
; FALSE if LP11 Printer output. TRUE (only) if output is to the S100_Parallel_IO
Board.
S100_ONLY: equ FALSE
; <----- If TRUE will skip checking to see if console IO should go to the UART
; will always sent to Console IO board (Switch K10 is ignored on the CPU board).
ODT_ONLY: equ FALSE
; <----- If TRUE will skip checking and always send console IO to the ODT UART
The links below will contain the most recent versions of the above software.
Note, it may change over time and may not correlate
exactly with the text in the article above.
