800xl pbi interface

[universal2600]

Hi just a quick question, is  how easily could one interface a ay-3-8910 via pbi (also is the pbi capable of driving a Tia from a 2600), to add enhanced sound, and an extra port which could also be utilized for bankswitching purposes (ram or more i/o devices [cowbell]), 

[Rybags]

800XL PBI doesn't supply external power by default so you either add it to the relevant pin or power your device externally.

It presents all the address+data lines but there's no decoding.  So you need to deduce when a relevant area is being accessed, e.g. $D6xx.

For replacement Ram or Rom there's the /Extsel line I believe you pull low which tells the computer the memory access will be serviced externally.

 

Extra devices like you mention - yes, shouldn't be a problem.  The /IRQ line can be driven but not /NMI.  Audio in gets mixed with the TV audio out the same way as the audio from the serial port.

[universal2600]

1 hour ago, Rybags said:

800XL PBI doesn't supply external power by default so you either add it to the relevant pin or power your device externally.

It presents all the address+data lines but there's no decoding.  So you need to deduce when a relevant area is being accessed, e.g. $D6xx.

For replacement Ram or Rom there's the /Extsel line I believe you pull low which tells the computer the memory access will be serviced externally.

 

Extra devices like you mention - yes, shouldn't be a problem.  The /IRQ line can be driven but not /NMI.  Audio in gets mixed with the TV audio out the same way as the audio from the serial port.

Makes sense, well my 800 has a 256k Newell board (ramdisk switch for original and "Sparta" I assume for Spartados?) So ram isn't really an issue, mainly I was thinking of using the 8910 via pbi to Port the Tia address space, and also it's control signals , and use the pbi databus to communicate to the Tia, pretty my 6502 Atari project in a nutshell, minus a 6532, this would be a "functional prototype", also use irq for Tia rdy for syncing writes, 8 channel sound with 2600 "emulation"

Edited April 25, 2020 by universal2600

[Rybags]

Not sure TIA would be worth the effort TBH.  Whether it could be used for video, unknown.  The A8 has a 3:2 clock ratio advantage but refresh cycles hurt timing a bit - though come to think of it, doesn't TIA require a ~ 3.6 MHz clock input?

A second Pokey and/or PIA would give more benefit at much lower complexity.

Edited April 25, 2020 by Rybags

[TGB1718]

Interfacing to the PBI is fairly straightforward, for safety, I buffer all inputs/outputs 

Data lines with 74244 octal bi-directional buffer.

 

and control/address lines with suitable buffer/invertor ttl chips.

 

You would have to add some logic to address the chip, so thats buffered as well

[universal2600]

Ok I see, yeah just looked at the pinout connecting it should be easy shouldn't need complex glue logic though I dunno if the Newell board (I believe it's 192k total as the board only has decode logic and replaces the upper 74ls151, and seems the base ram was replaced) will play nicely, I know I'll have to have some decoding logic for the 8910 (I know I need to generate iirc  a 4 bit control bus for bdir, my system is ntsc and so is my Tia (full 128 color Palette ?) so the Tia would need to run at ntsc colorburst 3.579545mhz, which I have some of those tiny smd oscillator which I would use for the clock, tia rdy would be connected to irq for sync, it's data bus directly controlled by the 6502, while it's address space would be ported via 8910 writes. I'm certain 8 channel sound would be possible, video would be interesting, if possible then one can make an XL "2600" compatible ,  though one would have to remap the code so it know where all the bits need to go, or some sort of "pseudo-emulator" that could translate address

 

PS technically isn't the ay-3-8910 a psg and pia in one...well psg and ported gpio, plus 8910 has more flexible sound compared to pokey, imho it's 1/3 Atari, 1/3 Nintendo, and 1/3 sid?

 

Edited April 25, 2020 by universal2600

[Rybags]

IMO and plenty of others, the AY/YM chip is inferior to all those you mentioned.

It has better frequency range than Pokey in 8-bit mode but lacks poly/waveforms.

 

Re decode - the Atari uses a 74LS138 to generate 8 signals as chip-select for each of the low $Dx pages which if you tap into can save some effort.

 

Doing anthing graphical with the TIA - CPU control is timing critical so I doubt it.  3:2 speed ratio and the refresh cycles all bunched together mean it just wouldn't be feasible.

[universal2600]

Interesting, I know the ay isn't the most powerful psg, but as mentioned it has features the pokey doesn't, (iirc some basic adsr and envelope control, and wider frequency range, I think ym chips have fm synth) and to me the ay chips can sound  kinda like a cross of nes, pokey, Sid mix depending what you're doing and sound demos I've listened to, one question if you eliminate the need for refresh (sram conversation) would it then be feasible to try driving the Tia, I do have some atmega8515, which could sit between the 6502 and Tia (I'd clock it at 21.47727mhz 6x the Tia clock to act as a hardware framebuffer, if using a 644), but mainly atm it's mostly for the 8 channel sound using spare parts

 

 

Edited April 25, 2020 by universal2600

[Rybags]

Sounds like some digital playback happening in that one.

The ST of course has the advantage in that it's CPU is fast enough to do that while still maintaining graphics and even gameplay.

 

In the 3 cases of AY, Pokey, SID, advances in knowledge and playback have been made in the modern day.

But still, I'll take Pokey any day over the AY.

[universal2600]

1 hour ago, Rybags said:

Sounds like some digital playback happening in that one.

The ST of course has the advantage in that it's CPU is fast enough to do that while still maintaining graphics and even gameplay.

 

In the 3 cases of AY, Pokey, SID, advances in knowledge and playback have been made in the modern day.

But still, I'll take Pokey any day over the AY.

True, unfortunately I don't have an ST, next computer I'd like to buy would be c128 only cause I had one when i was a kid, also a commodore Colt (I'm 23 btw which is the surprising part?), price wise I'd get a c64...any way this idea was based around my 6502 2600 project, since the xl pretty much has everything I need minus Tia, atmega, and GI,ay,ym, so I might as well simply connect them via pbi, It'd make debugging and writing code less of a hassle, essentially this would be equivalent nowadays as a prototype devkit I guess

Edited April 25, 2020 by universal2600

[Mathy]

Hello guys

 

Take a look at this.

 

Sincerely

 

Mathy

[kogden]

8 hours ago, Mathy said:

Hello guys

 

Take a look at this.

 

Sincerely

 

Mathy

That's really neat.  I just never really liked the AY much.  I grew up with the ST as well.  I always thought POKEY had more "character".  

 

Maybe I should try to build a quad POKEY cart for my ST.  I'd love to see what kind of cool things could be done with a POKEY driven by a 68000.

[Rybags]

I like how it has the asynchronous selectable clocks, so minimal effort required to port music across.

 

Pokey on ST - you'd need to derive a reasonable input clock frequency.

Since the ST is 8 MHz, a div by 4 gives 2 MHz which might be too much.  Div by 8 = 1 MHz which is probably a touch too low.

Some arcade applications used speeds around 1.4 MHz from memory which in fact probably gives a better range of frequencies in the 64 KHz mode.

[universal2600]

stereo ay via the cart port thats interesting, that would work though i'd like to have have access to the 64k of ported gpio space, plus i would be able to use more than 4MB of ram using the 2 8910 ports?