Finished checking and fixing up the diagnostic load file

FOUND ALL THE DIFFERENCES TO THE LISTING

I ended up with quite a few words that didn't match, although most of them are consistently different because of some corrupted test sequences towards the end of the code. Since the test sequences were a bit longer the address of data at the end of the program shifted, thus any instructions that referenced these locations did not agree with the listing. 

In addition to all the differences based on the shifted locations near the end, there was a single word that was incorrect - the value that caused our spurious error message. However, it was not just a matter of shifted locations for everything else. Some of the test sequences to be typed were alternatives to the code I discovered but seemed like it would accomplish the same purpose.

ALTERNATIVE TYPING SEQUENCES

The first deviations in test sequences began in the middle of the Backspace and Index test. This test begins by issuing a tab, then types backspace in reverse backing up from the tab column, then does a tab and types index with a line feed and backspace between each character so that it appears vertically on the page. 

The code I have in the file issues a character code that combines more than one control function in the same character, which isn't defined as valid in the programming documentation. Every control function has the low order bit set to 1. The other bits define which control function:

• 81 - carriage return
• 41 - tab
• 21 - space
• 11 - backspace
• 09 - shift to black
• 05 - shift to red
• 03 - line feed

Note that the functions above are a single bit set plus the low order one. My listing for the diagnostic accomplishes the index part of the Backspace and Index test by issuing an 11 then an 03, to backspace then linefeed. The load file has a single control character 13, which seems to combine the backspace and the line feed into a single command. 

Because the load file combines these commands, it is shorter by three words. That displaces all the sequences that follow (Auto Carrier Return, Rock, Roll and Twist) plus all the data and code that follows the sequences. One word was added to a data table, which consumes one of the three words that was gained by compressing pairs of movement commands into a single hybrid command such as line feed plus backspace. 

CORRECTED LOAD FILE FOR SINGLE CORRUPTED WORD

Since the typing sequences and related address shifting appear to be an intentional update made by IBM in order to fit a change in the same diagnostic test footprint, the only difference that seemed to matter was the constant for the desired Device Status Word (DSW). After the typewriter is commanded to type a character with an XIO Write instruction, while the mechanical operation is underway but before it completes. an XIO Sense Device should return a DSW that has both the busy and not ready bits set. The constant should have had both bits turned on, but it instead only had a bit for busy status. 

NEXT STEPS

With the file corrected, when I next arrive at the workshop I should be able to run the diagnostic without receiving the false error messages that were caused by the corrupted constant. I have some things to do that will delay my next visit to the shop, but once I am able to return I will load the fixed file and try out the typewriter.

I do have questions about the unorthodox combination commands that mix more than one movement command in the same XIO Write instruction. The reason I want to look closer is because the controller logic is sensitive to two feedback signals coming from the typewriter, which are -Twr CB Response and +Twr CrLfT Interlock, both of which are produced by multiple microswitches. 

Two of the typewriter movements, tab and carrier return, are variable duration events which depend upon pairs of microswitches to properly cover the entire duration. If the adjustments aren't correct, we could see a spurious edge on the signal that convinces the controller logic that the movement is complete even though the signal goes back to busy for additional time. 

I will put the oscilloscope on the two feedback signals and watch what occurs with the combination movement commands, hand coding an XIO Write to trigger the movement. If anything looks wonky, I will know the microswitch(es) to check and readjust.