Small alternatives to the W65C51 ACIA and W65C22 VIA

[billylegota]

I am trying to make a *small* SBC using the W65C02S6TQG (QFP-44) and want to use as little board space as possible. The WDC datasheets show that there is indeed a QFP version of both chips but I can't seem to find any distributors that carry them. Does anyone know where I could purchase some QFP versions of the chips or any alternatives that come in BGA or QFP form?

To be clear, I only need some sort of parallel interface controller and some sort of serial interface controller. I do *not* need them to be software compatible with the 65C22/51 nor do I need the timer portion of the VIA.

[GARTHWILSON]

The PQFP's might only be available directly from WDC. Give them a call with credit card in hand. Our topic on where to get the parts is at viewtopic.php?f=1&t=1953 which we try to keep up to date; but a search there for "PQFP" does not find any occurrences.

Some of the 65c22's counter/timer functions that come to mind other than just as a timer are:

• setting the speed of the onboard synchronous serial port
• event counter
• frequency counter (how many transitions counted on one counter/timer during the number of Φ2 cycles timed in the latches of the other?)
• watchdog timer
• producing a square wave, for example to produce a beep without the processor having to babysit it through the duration of the beep; or use as an external x16 clock source for the '51, which I've done for MIDI (musical instrument digital interface) which runs at 31.25kbps, 1/16th of 500kHz which I produced with the '22

I'm sure there are others I'm forgetting. Just because you don't need a regular timed interrupt doesn't mean you won't have any use for the timer/counters. I've used the 65c22's synchronous-serial port many times as well, even for RS-232 transmission with the speed governed by Timer2, and for a simple 9-level D/A converter useful for DTMF (phone touch tones) and even highly compressed speech with sound quality a little better than a lot of talking toys. There's a lot of this kind of stuff in the "Tip of the Day" column. The '22 also has interrupt-on-edge pins (CA and CB pins), and port pins can be used as as open-collector pins for things like I²C.

[BitWise]

Have you considered using one of the micro-controller versions of the processor like the 65C134 or 65C265?

They need only a few external components and have a number of peripherals built in including ACIAs.

WDC's own development boards for these are much better priced (~$100) than the full microprocessor equivalent. The 65C265 board in particular is quite fun to work with and easy to expand.

[Dr Jefyll]

BitWise wrote:

Have you considered using one of the micro-controller versions of the processor like the 65C134 or 65C265?

Good idea. And a quick check at Mouser shows they presently have stock of both the 65C134 and 65C265, and the corresponding SBC's -- see here and here.

No PQFP's, I'm afraid. But, as Andrew noted, these chips include peripherals. So, if you wanna build something small then they're definitely worth considering. Be warned the datasheets are very poorly organized, but some folks here (Andrew and Scot, IIRC) have been working on untangling the details.

-- Jeff

[billylegota]

GARTHWILSON wrote:

Some of the 65c22's counter/timer functions that come to mind other than just as a timer which come to mind are:

• setting the speed of the onboard synchronous serial port
• event counter
• frequency counter (how many transitions counted on one counter/timer during the number of Φ2 cycles timed in the latches of the other?)
• watchdog timer
• producing a square wave, for example to produce a beep without the processor having to babysit it through the duration of the beep; or use as an external x16 clock source for the '51, which I've done for MIDI (musical instrument digital interface) which runs at 31.25kbps, 1/16th of 500kHz, which I produced with the '22

I'm sure there are others I'm forgetting. Just because you don't need a regular timed interrupt doesn't mean you won't have any use for the timer/counters. I've used the 65c22's synchronous-serial port many times as well, even for RS-232 transmission with the speed governed by Timer2, and for a simple 9-level D/A converter useful for DTMF (phone touch tones) and even highly compressed speech with sound quality a little better than a lot of talking toys. There's a lot of this kind of stuff in the "Tip of the Day" column. The '22 also has interrupt-on-edge pins (CA and CB pins), and port pins can be used as as open-collector pins for things like I²C.

I am currently planning to simply use the VIAs (or whatever I choose to use in their place) as GPIO controllers and then make separate boards for sound, etc (in a stackable, shield-like format).

As for the 65C51, I think I will either use a larger CPLD and integrate a UART or use a SPI UART controlled by a VIA.

[billylegota]

BitWise wrote:

Have you considered using one of the micro-controller versions of the processor like the 65C134 or 65C265?

They need only a few external components and have a number of peripherals built in including ACIAs.

WDC's own development boards for these are much better priced (~$100) than the full microprocessor equivalent. The 65C265 board in particular is quite fun to work with and easy to expand.

I like having a seperate MPU, RAM, and ROM as it makes the system feel less like a "magic chip that does everything".

[Martin_H]

billylegota wrote:

I like having a seperate MPU, RAM, and ROM as it makes the system feel less like a "magic chip that does everything".

The microcontroller versions of the 6502 and 65816 have internal registers that allow the use of external RAM and ROM.

[billylegota]

Martin_H wrote:

billylegota wrote:

I like having a seperate MPU, RAM, and ROM as it makes the system feel less like a "magic chip that does everything".

The microcontroller versions of the 6502 and 65816 have internal registers that allow the use of external RAM and ROM.

But I want all of the RAM, ROM, and IO to be external. It just feels less cheaty.

[BigEd]

We visit these tradeoffs pretty often here. Some people want to build hardware from small primitives, some want to have hardware so they can get on with building systems and software. It's a matter of personal preference. No need to put a value judgement on it.

[Dr Jefyll]

billylegota wrote:

To be clear, I only need some sort of parallel interface controller and some sort of serial interface controller.

Both of these can be realized using Serial Peripheral Interface (SPI). SPI chips tend to be small, partly because fewer pins are required (as compared with a chip whose host interface is parallel). For a small system you'd probably want to use a "bit-bang" approach rather than including a parallel-to-SPI controller IC.

Even bit-banging requires a small, up-front hardware investment. Your system needs to output CK, MOSI and CS and needs to input MISO and IRQ. That can be done with less hardware than you might expect, as various shortcuts are possible (especially on the 'C02). Once the bit-bang SPI is in place you can easily add whatever serial & parallel chips appeal to you. That's where the initial investment can pay off several-fold.

Alternatively (or additionally) you could have your system talk to ordinary shift register IC's for the parallel IO. And asynchronous serial communication ("RS232"-style) can be bit-banged without including a UART. The tradeoff in that case is trickier software, since specific timing requirements apply (unlike SPI). Forum topics exist which discuss bit-bang asych in detail. Depending on your frame of mind, you may find bit-bang asych to be either good sport or a tiresome limitation. It's all about tradeoffs, as Ed said.

FWIW, lately I've been fooling around with an SC16IS750 SPI UART (for which I made my own breakout board). The length of this 24-pin IC is less than the width of an ordinary .3" DIP. And it includes 8 bits of parallel IO. Other SPI UARTs are available, of course -- some of which can operate from a 5V supply (the SC16IS750 needs 3 volts).

cheers,
Jeff

[billylegota]

Dr Jefyll wrote:

billylegota wrote:

To be clear, I only need some sort of parallel interface controller and some sort of serial interface controller.

Both of these can be realized using Serial Peripheral Interface (SPI). SPI chips tend to be small, partly because fewer pins are required (as compared with a chip whose host interface is parallel). For a small system you'd probably want to use a "bit-bang" approach rather than including a parallel-to-SPI controller IC.

Even bit-banging requires a small, up-front hardware investment. Your system needs to output CK, MOSI and CS and needs to input MISO and IRQ. That can be done with less hardware than you might expect, as various shortcuts are possible (especially on the 'C02). Once the bit-bang SPI is in place you can easily add whatever serial & parallel chips appeal to you. That's where the initial investment can pay off several-fold.

Alternatively (or additionally) you could have your system talk to ordinary shift register IC's for the parallel IO. And asynchronous serial communication ("RS232"-style) can be bit-banged without including a UART. The tradeoff in that case is trickier software, since specific timing requirements apply (unlike SPI). Forum topics exist which discuss bit-bang asych in detail. Depending on your frame of mind, you may find bit-bang asych to be either good sport or a tiresome limitation. It's all about tradeoffs, as Ed said.

FWIW, lately I've been fooling around with an SC16IS750 SPI UART (for which I made my own breakout board). The length of this 24-pin IC is less than the width of an ordinary .3" DIP. And it includes 8 bits of parallel IO. Other SPI UARTs are available, of course -- some of which can operate from a 5V supply (the SC16IS750 needs 3 volts).

cheers,
Jeff

I was considering doing this with the PLCC version of the VIA but have instead opted to simply make an ACIA equivalent in my CPLD.