Question about PDP 11/40
- View SourceFor those who know about PDP 11/40's
This project had been on the back burner, but I thought I'd mess with it this week. I have been able to write and read back memory using the console. I have also been able to run a "chase the lights" program. System is working as it was originally when I got it and it's in a nice air conditioned environment. I have been working on a memory map. I assume emply RAM locations are identified with a FFF FFF FFF FFF / 000 000 000 000 pattern as I walk up the memory. The switch register is present at 777 570.
Here is what I have installed:
CARD SLOT POSTITION
empty 1 -- (IF PRESENT WOULD BE USED FOR A 7239)
empty 2 -- (IF PRESENT WOULD BE USED FOR A 7298)
7232 3 A-F (U WORD)
7231 4 A-F (DATA PATHS)
7233 5 A-F (IR DECODE)
7235 6 A-F (STATUS)
7236 7 A-F (TIMING)
7236 8 A-F (MEMORY MANAGER)
672A 9 D (GRANT CONT.)
UNIBUS 9 A-B (RIGHT SIDE OF UNIBUS)
UNIBUS 10 A-B (LEFT SIDE OF UNIBUS)
M7856 10 F-C (RS232 WITH 19.2 OPTION?)
G7273 11 C-D
7891 12 A-F (64k MEMORY)
M9312 13 A-B (ROM CARD)
672A 13 D (GRANT CONT.)
Things are slow because the original 8K core has been upgraded with a 64K board. I am not sure if the core is bypassed or supplemented, but I assume the former. This means that my "stock" docs about the 11/40 are not very useful. To make it a little harder, the 11/40 docs refer to the LA30 DecWriter but I have a newer LA36 Decwriter II terminal that has in turn been upgraded from 300 baud to 1200 (according to a sticker). I am flying a bit blind here.
With all that in mind I wish to explore the terminal interface using the M7856. I don't have the M7856, 7891, or M9312 docs (still trying to find). I have the original bootstrap ROM that came with the M9312 still present as it was originally, and the seller of the system was able to get to a " @ " prompt with it. I was told to load the address 165144 to activate the terminal bootstrap, but when I examine this location, nothing appears to be loaded into memory (just blank RAM: FFF FFF FFF FFF/ 000 000 000 000 etc.) at 165144. When I attempt to activate the ROM (halt, load address 165144, depress enable, and then start). There is no change to the data in memory location 165144. Is there someplace else I should be looking? Should it be 765144 because of the memory management card (7236)? Whatever the case I do not get a response from the "terminal". I understand from my notes of my conversation with the seller that to use the LA 36 DecWriter II with this particular 11/40 I will have to change the baud rate jumpers or switches on the M7856 from 19.2K to a lower setting for the terminal. So, for the time being I am using a computer with the windows terminal program set for VT 52, 7 bits no parity, and 19.2K baud because I believe that's what it's set for. I have also tried other settings such as 8 bits no parity, VT 100, etc. I am confident that the computer running the terminal program is looking at the correct COM port. Knowing what I know, I would not expect any terminal output yet anyway because there is no program loaded, yes?
I have worked hard to find answers and docs on my own, but I am at a stand still at the moment. Any tips you may have would be appreciated.
NOTE: There's a note on the DEC terminal to indicate that it was upgraded to 1200. In local mode the DEC terminal works OK.
In the meantime, I will toggle one memory location at a time to map out the 64K in search for code/data.