A Question About 6532 Chips...

[DavidMil]

Was the 6532 chip (C010750) RIOT chip a version of the 6520 (C014795) PIA chip? The reason I ask is that in the 850 interface are two of the 6532 (Riot) chips (A103 & A104).

The field repair manual calls them PIA chips, but the chips are clearly marked C010750 which are RIOT (RAM I/O Timer) chips. As usual, I'm lost and confused...

 

DavidMil

 

 

 

[thorfdbg]

Was the 6532 chip (C010750) RIOT chip a version of the 6520 (C014795) PIA chip?

No, completely different chip. The RIOTs have 128 bytes static RAM, a timer, a primitive serial port option and a couple of I/O lines. It's a multi-function chip for cheap designs.

 

The only similarity to the 6520 are the two I/O ports it has (similar to the PIA). The reason why Atari might have picked them is because no additional RAM is required. The RIOT Ram acts both as zero-page, stack area and I/O buffer.

[Bryan]

Yeah, same family of chips but with different features.

[+mytek]

It's a very nice chip, and when coupled with a CPU, an EEPROM, and very little else gives you a complete micro computer.

 

- Michael

[+DrVenkman]

It's a very nice chip, and when coupled with a CPU, an EEPROM, and very little else gives you a complete micro computer.

 

- Michael

As demonstrated by the Atari 2600. . And when you add a floppy disk controller chip and some ROM to hold firmware, it makes a decent floppy drive system (see, e.g., the Atari 1050).

[+mytek]

I think it was Rockwell that combined all of what I described into a single chip creating essentially a 6502 based microcontroller. Unfortunately it never caught on, otherwise we might be using a miniaturized version of this instead of AVR's or PIC chips today (wouldn't that have been sweet).

 

- Michael

[Rybags]

I think the 6520 PIA as used in the computer was probably the lowest specced of the entire family (including VIA, CIA, RIOT).

 

It's barely more than a couple of bidirectional latch sets with that extra bit of peripheral and interrupt generation support.

Sort of a pity we didn't end up with something a bit better - just a couple of timers with 1-shot/continous mode and optional IRQ generation would have been really nice.

[Bryan]

I wonder if there was much cost difference between the chips.

[Rybags]

I imagine in the design stages there might have been a fair gap between 6520 and the higher end stuff. But we're talking a time when even the 400 was over $500 in the US and the 2600 probably half that or more.

Compare that to the late 1980s, the 2600 board and components in total probably cost less to make than the plastic case and packing box it came in.

[ricortes]

Me too, another RIOT fan. Just add a ROM and you are ready to go for a 3 chip 65xx system. There were a few other interesting chips that never really made it to prime time. Some of this is really esoteric for I/O guys. There was a ~super 6520 type device with 3 ports instead of two. I always thought this would be great for a IDE type interface but with everything going SD/SATA the thought is as obsolete as me! There was also a DUART offered in several packages from just the two serial ports<28 pins?> to a 40 pin device with the extra pins serving PIA type function.

 

I thought the chip used in the ICD PR:Connection was a 65xx type processor core with RIOT/PIA features on chip??? I'm sure there were others that were 65xx derivatives.

[+mytek]

Here's an example of the Rockwell 6501 micro-controller being used in a DIY single board computer...

 

 

www.obelisk.me.uk/electronics/R6501.html

 

Rockwell 6501XX Datasheet: R6501AJ_to_R6501QE.pdf

 

This 6502 instruction set compatible micro-controller has 192 bytes of Static RAM built-in, 4 I/O ports similar to a PIA, Full-Duplex Serial Port, and two 16-Bit Programmable Timers. All it needs is an external ROM and Crystal to be up and going. Check out that unusual IC socket

 

- Michael

 

[DavidMil]

After reading all your feedback I decided to do some online research. According to Rockwell, the 6532 also has eight parallel lines (PA0 to PA7) which drive the printer port on the 850.

I always thought that the RIOT chip only had a couple of I/O lines too. See below:

 

I guess I'm still learning things...

DavidMil

Edited May 24, 2017 by DavidMil

[Bryan]

It actually has 2 8-bit ports like the 6520. The 2600 uses some of the 2nd port for the console switches.

[+DrVenkman]

It actually has 2 8-bit ports like the 6520. The 2600 uses some of the 2nd port for the console switches.

 

Yep. One of the obvious signs of RIOT failure (especially on 4-switch units, as I've discovered!) is failure of one or both of the player Difficulty Switches. Since many games don't vary difficulty in a visible way, and some games don't use them at all, a lot of people don't notice the failure. But put in SPACE INVADERS, select a two player game, toggle the switch for each player during their turn and you can test this - in Space Invaders, "A" difficulty sets the player's cannon to double-wide. If a 2600 difficulty switch seems "stuck" after you've cleaned it and verified the board trace, I can almost 100% guarantee it's because the RIOT has started to fail.

[Wrathchild]

In the 90's I worked on a swimming pool controller that used an M37450 micro which, having the A8 / 6502 background, I liked a lot for all the 'missing' opcodes it provided such as inc/dec the accumulator, bit set/clr & basic Mul/Div operations.

[Bryan]

In the 90's I worked on a swimming pool controller that used an M37450 micro which, having the A8 / 6502 background, I liked a lot for all the 'missing' opcodes it provided such as inc/dec the accumulator, bit set/clr & basic Mul/Div operations.

The 6502 is mostly limited by it's small instruction LUT. If we just could have stuck a few more sequences in there....