As I look across different 6502 projects I see two different methods of connectivity for Character LCD displays. Some projects show them hanging off the ports of a VIA and some projects have them directly on the system bus with the enable being driven by address decoding.

I plan on using a 4 x 20 character display that I have here in a drawer, standard 4 bit interface, nothing fancy. In my mind if I have the address space (or granular control of the address space) it would be more efficient to put the display right on the bus vs. on a VIA and be able to keep that VIA port available for other uses but not sure if I'm missing on a benefit of leveraging the VIA?

Thoughts, comments, is it really just a preference thing?

Check the datasheet, if you have it. I think there's a chance the LCD will be quite slow, which is fine if you drive it from a VIA, but means you need to deal with RDY or with clock-stretching if you drive it directly off the bus.

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The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Even with the LCD attached you may still be able to attach other device(s) to the same 4 port lines. As a simple (though perhaps unlikely) example, you could attach *two* LCD's.

Of course, the VIA would also have to provide a Strobe or Write signal to each LCD, and these signals would have to be unique to each LCD, not shared. But the total number of pins for two LCD's would be 4+2 = 6 port lines -- not 4+1 + 4+1 = 10. I hope that explanation makes sense! It would also be possible to attach a device driving data in the other direction, using the 4 VIA lines as inputs.

Just thought I'd mention these possibilities. I'm not saying you ought to multi-task some of the VIA port lines, but the idea may be appealing, depending on your own priorities.

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Acorn's BBC Micro also does a lot with one of the VIAs:
- joystick button inputs, and lightpen strobe
- ADC completion signal
- two bits to control video's memory map
- * TMS5220 speech chip (optional)
- * sound chip
- * keyboard scanning and control
- 2 keyboard LEDs
- vertical sync indication (for a per-frame interrupt)

The three marked with * sit on an 8 bit databus which uses the A port. On the B port, four bits are used as inputs to a 74LS259 which gives (I think) 8 bits of set/reset control, which are in part used as chip selects and write enables for devices on that slow bus.

The keyboard itself is a bit complex, and includes an 8 bit readable DIP switch for boot options.