Hi All;
Dave, Thank You for the next Installment..
I had made an earlier post, but somehow I lost it..
Dave, as per Your statement, I have put in a Temporary crystal for my Frequency to the UART and it is at a steady 4.80005 Khz..
I will wire it in later..
But, all of a sudden the Reverse Echo program fails..
I am going to look into things.. possible a stray wire or something like that..
I found the problem, I had forgotten to hook up the Loop-back connection..
It has at present a faster clock, and I will retry the echo program again, just in case..
No, it still fails, same place..
I am going to try Dave's alternate program, and report what it shows..
0000 6044
0001 6032
0002 7200
0003 7402
0004 6034
0005 7402
0006 5000..
After I run it, that is after putting in a 0101 in the Accumulator, It shows an 'A' on the screen..
Then after the next continue, after the 6034 at address 0004..
It shows a '0001..
I even slowed it down, to my regular fast clock.. Same thing.. I even tried putting in a 'B'.. Same output, '0001..
What I don't know is 'if' the '0001 is correct or if it should show what I originally entered into the Accumulator..
"" Have you also tried my ECHO program from post #377 (PC to PDP-8 UART, loopback internally via PDP-8 software back to UART and back to PC)? Type a character on the PC - it should echo back on the PC. ""
Yes, that is the one that fails, still loops at address '0001 and '0002..
"" When you say you have tried the interrupt program - do you mean the one in post #382? ""
Yes..
"" I can give you a few things to look at in the short-term (I will be out for most of the day today). No problem, I will be gone from about 11:00 till 2:00..
When you press a key on your PC - and the character is received by the UART - Pin 19 of the UART should go from '0' to '1'.
"" should go from '0' to '1'. ""
It stays at '0'..
"" and the character is received by the UART ""
YES.. pin 20 on the UART..
E12 pin 8 (PINT) should go from '0' to '1' at the same time (this gate merges the interrupts from the UART Tx and Rx). Just check that pins 9 and 10 of E12 (inputs on figure 1 of the TTY interface schematics) are both '1' before you start (signifying no interrupts are pending).
E12 pin 8 (PINT) should be wired to schematic LD21 E5 pin 12. This pin should also go from a '0' to a '1' when you enter a key on your PC.
Assuming interrupts have been enabled by an ION instruction (6001) pin 13 of E5 should already be a '1'.
An incoming interrupt from the Rx half of the UART should, therefore, drive pin 11 of E5 low (/I.IE) - which (in turn) is wired to our favourite place - pin 8 of J7 on schematic LD11 (the F/A state machine). ""
I am going to make another change to the Board, I am going to monitor with Led's the error status pins..
I Just found something interesting, from my Status Led's, which monitor pins 13, 14, 15, 19, 20 and 24..
And when monitoring pin 19, it goes up and down when running Dave's reverse echo program,
But, stays the same when running the Interrupt program, which means the Interrupt is not getting thru to the computer..
As pin 19, doesn't go high..
Here is a picture of the I/O Board, with all of it's latest gadgets..
I tried the RIM Loader, and I think it fails for the same reason, that Echo fails..
I am starting a new posting.. Part 4...
http://www.vintage-computer.com/vcforum/showthread.php?50593-Build-your-own-PDP-8I-Part-4
THANK YOU Marty