Re: New firmware for PLC TIB DD-001 3.5" drive

Witam Maciej,


> I prepared a new firmware for TIB DD-001 ....

That is a coincidence! Two weeks a go I ran into five GM82C765B ICs, but 
the 40-pin version, not the PLCC. I don't know how anymore but the day 
before I ran into Steve Gray's site with the clone so seeing those ICs I 
immediately knew where to use them for. But mine were 40-pin so I had to 
make a new PCB. And here I ran into a weird difference: the 40-pin 
version doesn't have the 'Disk Change' pins. Bummer.
That was reason for me to go through the code to see where it was used 
but I couldn't find it. OK, a part hadn't been disabled yet but 
filtering bit 7 shouldn't have been easy to miss.

So my question: have you run into a check of these pins?

The original 765 used by the PC-XT hadn't these pins either so I asked 
around. If another request for access to the floppy wasn't within two 
seconds of the last one, the ID of the drive was checked. I haven't 
found anything (yet) that looks like a check but there must be 
something, if it was just a read of the floppy for the very forst time.


Here are some (new) notes I put in my own disassembly:
; - only a 3,5" 720 KB DD FDD can be used, not a 5.25" 360 KB one
;   ##### can that be changed?

; - only ONE drive can be used
;   ##### can that be changed?    ---> you already mentioned using a 
jumper, but what about software?

; - a directory sector is stored in the RAM under the $Dxxx area
;   ##### what about loading big programs, won't they overwrite things?

; - Some RS232 variables are used, meaning: we cannot use RS 232 
anymores
;   2023-08-09: ??? which ones?
;   ##### if so, what about using more tape variable etc.?

; - bad: I/O port of 6510 is manipulated but not restored with original 
value
; - bad: video control register is manipulated and not restored
; - inconsistent use of Carry for reporting an error

; - in general: the programming could have been done more efficient

Of course I thought about some improved hardware with extra RAM but, 
let's face, who will be waiting for it?


-- 

Kind regards / Met vriendelijke groet, Ruud Baltissen

www.Baltissen.org