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Tandy 1000 SL Jumper Settings

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CarlosTex

Experienced Member
Joined
Mar 26, 2013
Messages
272
OK, so i read that some later model Tandy 1000's have a jumper for VSYNC IRQ5.

On my Tandy SL there's no such jumper. Checking the tech notes manual for all Tandy machines i found this for the SL:


E2-E3 (Default) Sets IRQ 5 for the hard drive and IRQ 2 for
the video.
E3 -E4 Sets IRQ 2 fur the hard drive and IRQ 5 for the video.
It is really not recommended to use this setting. Not
all software will run correctly on IRQ2.
Click to expand...

All other later machines seem to have this too and i was wondering about this. Which setting is thhe best? Will any of the settings have less/more game compatibility?
 
No because i've read from other vintage computer enthusiasts that IRQ5 was used for video by older Tandys hence my question. The tech notes info conflicts with this.

Also why doesn't the SL have the VSYNC jumper like the TL's and RL's?
 
IRQ 5 for video is the one compatible with the PCjr. However, almost no software uses this, so you should set IRQ 5 for the hard drive, which is typical for XT-class systems.
 
Can you think of examples where this is a problem?
Is this because certain software disables certain interrupts, and assumes that they can safely turn off IRQ 2, but not IRQ 5?

Because I can't imagine the video interrupt or HDD interrupt being a problem under normal circumstances. Video interrupt is never used, and the HDD is handled by the BIOS, so it does not depend on any software, drivers or anything, it just works.
 
I have IRQ 5 connected to VSYNC in my 1000 RL for some early-game compatibility. In correspondence with NewRisingSun over the years, a handful of PCjr/Tandy titles have been identified (and tested) as requiring it, including Boulder Dash I & II, Demon Attack, Ghostbusters, and Touchdown Football.

If you don't have any ISA-based peripherals in the SL that need IRQ 5 otherwise, there wouldn't be any downside to jumpering it similarly.
 
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