Posted By
TLC
on 2011-09-16
17:02:17
|  Re: Joystick not working in either port
You can test whether the TED is toast (...better said: if it has the infamous "keyboard latch is broken" symptom) if you're not afraid of typing in a couple of commands.
Boot up the machine, go into TEDMON ("monitor" command from Basic, or press Run/Stop together with the Reset button), and enter the following code:
A 2000 sei
lda #$00
sta $fd30
sta $ff08
ldx $ff08
stx $ff15
jmp $2006
Now, start it with G2000 . The background color should change if you press some keys.
Now, press reset, go back into tedmon, and modify the routine like this:
A200f jmp $2009
Then start the code again (G2000).
...Now, if you can _still_ notice the background color to change with keypresses, the input latch of your TED is toast.
(That common failure is effectively the TEDs unability to sample and latch the keyboard matrix input port at the exact point when (as a strobe) the $ff08 register is _written_ to. That capability is strictly needed for joystick port handling - whilst, as you can see, isn't fatal, as long as only keyboard scan is needed).
If the above test shows that your TED works, you can still suspect a couple of things - but IMHO it's better to test new gadgets using known to work hw ie. a known to work Plus/4 (if one's available).
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