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Patching OS disks for RS Doubler vs Percom Doubler (and others)

T

Tibs

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Joined
Dec 10, 2016
Messages
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Ive been poking around the code on DOSPLUS and reading up on the different methods used to switch between the two, mainly because I am just interested. I know that DOSPLUS has the patch on 3.5, and LDOS has the /CMD files to load the drivers for either, but having 2.7DD boot on a Percom doubler was kind of funny when it wouldn't work on my RS Doubler.

What I have not found in all the scouring is how people knew to patch TRSDOS 2.7DD to work on a PERCOM and vice versa for some of the other DOSes on the RS Doubler.

Was there a list of the patches needed or was it just a tribal knowledge thing? (DOSPLUS has one called RS/TXT and I disassembled SYS0 and SYS1 to see what they changed and why). Basically they change the switch between SD/DD values written to the port, but I didnt see where they actually did the write precomp change that the RS service manual talks about.

I have both types of doublers, and the one DOS I dont have that works on both is TRSDOS 2.8. Only have that for the RS Doubler.

For the differences in DOSPLUS here is the code:
Code: 
PATCH SYS0/SYS.SYS:0		Others			Tandy
A=48A0H,F=FF,C=80			LD    A,0FFH		LD	A,080H	SELECT DOUBLE
					BIT	7,(IY+0BH)		BIT	7,(IY+0BH)
					JR	NZ,48A9H
A=48A8H,F=FE,C=A0			LD	A,0FEH		LD	A,0A0H	SELECT SINGLE	
A=48A9H,F=CDBE48,C=32EE37	CALL	48BEH			LD	(37EEH),A	OUT TO MEMORY MAPPED PORT INSTEAD OF CALL TO BELOW ROUTINE
A=48ADH,F=00,C=E0			LD	A,00H			LD	A,E0H
					LD	(37EEH),A		LD	(37EEH),A
					LD	A,0DOH		LD	A,0D0H
					JR	48BEH
					LD	A,(IX+00H)
					DI
					LD	(37ECH),A
					
					

PATCH SYS1/SYS.SYS:0
A=50F9H,F=3EFE32EC37,C=3EA032EE37

					LD	A,OFEH		LD	A,0A0H	SELECT SINGLE
					LD	(37ECH),A		LD	(37EEH),A	OUT TO MEMORY MAPPED PORT
 
lafos said:
I remember looking for this years ago with no real success. There's an article about building a doubler on Ira's site

http://www.trs-80.com/wordpress/zaps-patches-pokes-tips/hardware/

It does not cover the RS doubler, but discusses the density select routine for Percom.
Click to expand...

Yeah, found that. The LNW manual and the RS Service Manual tells you how to do the options of the adapters.

The NEWDOS ZAPs tell you how to patch it for RS doublers, and does show the example on the write precomp part. I guess I'll screw around with my TRSDOS 2.8 master (well a backup) and see if I can find the machine code and update it. Someone figured out what to change on the 2.7DD disk, and I may spend the time comparing the system files between them as well to find it but was hoping someone had it still. The "fun" part on TRSDOS 2.7, 2.8 and 1.x is that you have to find out what sectors and dump them to files to really make it easier.

I think the only thing we dont have is a 2.8 disk that works on non RS Doublers in the various archives.
 
Please consider writing about the patches you find and develop. I'm sure there will be others interested in the information.
 
Absolutely will do. Just gotta fix my Model I now hehe, I think a tristate died after a RAM chip gave up the ghost.
 
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