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Bad bit

J

joeatact

Experienced Member
Joined
Nov 29, 2023
Messages
256
I cannot figure out which bit is bad once have told me how to do the conversion, but I lack something need some help
Should be @9 not ;B.
 

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You lookup the ASCII table for the character that is being displayed, obtain the hex number, and convert that into binary.

Code: 
@ = 40 = 0100 0000
B = 42 = 0100 0010

9 = 39 = 0011 1001
; = 3B = 0011 1011

In both cases, data bit 1 (counting from bit 0 on the right) is stuck at a '1'.

Dave
 
Thanks for the reply. I think I finally got it now again thanks, Joe.
 
SN Error is a SYNTAX error, so the keystroke(s) that it is getting is not valid.

Look for bad or defective flex cable, or bad solder joints on the Keyboard or Motherboard.

You are getting there.........keep plugging away.

Larry
 
Funny, there’s no keyboard attached. Only works when I plug-in the first prom. The diagnostic runs fine in the local in the first location, but not the regular bias.
 
The only way to know if the ROM's are good is to read their contents and compare with
the same Version File(s) on the Internet. But, in all my years since I bought my TRS-80
Model 1 in the 1980's, I've not come across a bad ROM.

Larry
 
What would it take to update 1.2 to 1.3 in the 3 rom set? Could someone help me?
 
I've noticed some other small board on the back of your motherboard. Do you know what
that is and what it's doing? I don't recall ever seeing that type modification.

Are you familiar with the Arduino MEGA 2560? I have some software for it that can read
those ROMS using an Arduino.


Larry
 
It’s for the tape drive circuit. Here is what I read from the eprom. (rename to .bin)
 

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It appears that your first 2048 bytes are the same as my Ver 1.1 ROM A. Bytes from 0x800
to the end are missing. Are you sure you have A12 connected to the Address Pin for
Chip Select being LOW = CS*

If the first half is correct, it's a safe bet that the last half is correct.

Larry
 
Jow,
How many wires does your 3 Chip ROM have going to it? It either has 4 or 6.
Also what color wire is on each Solder pad?

4 Conductors
A11 -
A12 -
A13 -
ROM* -

6 Conductors
GND -
A11 -
A12 -
A13 -
ROM* -
+5 VDC -

That will give me a clue about your Motherboard.


Larry
 
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Picture one from right the left yellow green orange and red picture two you can see where the wires go in the back of the motherboard which seem to be right. I’m wondering when I hook up the bias he thinks it’s getting a keystroke. It’s like the ( is displayed after memory size and then a cr. Maybe there’s a logic problem.
 

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Looking at the keyboard schematic, I see the following keys are all on the same column (driving KC0):

'@' 'H' 'P' 'X' '0' '8(' <ENTER> <LEFT SHIFT> and <RIGHT SHIFT>.

It is possible that you have a fault somewhere with either the KC0 signal being connected to 0V (thus the computer thinking this row of keys is active all the time) or there is a fault with the tri-state inverting buffer (Z3 pins 2 or 3) driving KC0 onto D0.

See: https://billr.incolor.com/trs80sch-sheet1of2-part5of5.GIF (on the assumption this schematic matches your specific machine).

Dave
 
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