Challenge : Modern serial board (quad?) for RC2014 ?

[rwd...@gmail.com]

I am hoping somebody has or will design a PCB for RC2014 with quad serial, using a chip in current mainstream supply from quality vendors (Mouser etc)

e.g. perhaps(but not necessarily) using  ST16C554/554D 2.97V TO 5.5V QUAD UART WITH 16-BYTE FIFO, PLCC flavour.

The reason for this is that a number of people have expressed interest  in MPM, FUZIX etc with multiple serial connections, and BBS systems.

I personally would like a system with at least 3 serial ports for console, printer and kermit or cp/net.

Ideally the chipset would be backward compatible with ACIA 68B50 so that various existing ROMs can still work with one or two serial connections (e.g. from Spencer Owen, Steve Cousins, Phillip Stevens, Wayne Warthen).

A design should allow software selectable baudrate, hopefully on a per port basis but that may be pushing a bit too much.

Since the new chip might be plcc in a socket to avoid smd soldering, then use of a plcc fpga/cpld etc to consolidate associated logic is not unreasonable.

Pushing  to keep functional back compatibility with legacy serial might make this adhere to "retro" flavour and keep purists on board.

This post was born out of problems I am having with my new 61f ACIA serial board, where the only uart chips come out of China, and I wonder about the quality. I notice on FB someone posting a problem with ACIA RC2014 Mini, where the symptoms, like mine, are lost data at 115200, easily and often, so that download of text to feed into download.com won't work. In my case I have tried multiple usb/serial devices.

I hope that someone may be inspired to create such a board, but failing that, at least input to show whether such an idea can be workable would be good. It is of course possible that in the huge world of rc2014 that someone has something close or equal to this coming through the system.

Richard

[Alan Cox]

On Wed, 29 Sept 2021 at 19:19, rwd...@gmail.com <rwd...@gmail.com> wrote:

I am hoping somebody has or will design a PCB for RC2014 with quad serial, using a chip in current mainstream supply from quality vendors (Mouser etc)

Been there, done that 8)

See https://hackaday.io/project/167720-rc2014-quad-uart

Also dual port 16C255x

https://hackaday.io/project/170819-16c2552-dual-uart-for-rc2014

Ideally the chipset would be backward compatible with ACIA 68B50 so that various existing ROMs can still work with one or two serial connections (e.g. from Spencer Owen, Steve Cousins, Phillip Stevens, Wayne Warthen).

ROMWBW already supports a bunch of different serial devices as does Fuzix.

A design should allow software selectable baudrate, hopefully on a per port basis but that may be pushing a bit too much.

16C255x and XR82C684 designs can do that on chip.

Alan

[Tadeusz Pycio]

True, an overclocked ACIA is the least happy solution. There are many far better designs in the community, probably all the chips I know that support serial ports are available. I personally use XR88C681, but they are very hard to find, but those modules that use Z80-SIO work just as well, for example SC104 or SC132.

[Bill Shen]

Interested to see what's currently available for quad serial port.  I have a large stockpile of OX16C954 (obsoleted part) and built a RC2014 board that works with Z280RC (Z280), CB030 (68030), and CRC65 (6502): https://www.retrobrewcomputers.org/doku.php?id=builderpages:plasmo:quadser

OX16C954 is an impressive quad serial device: 128 byte FIFO each channel, software compatible with 16C55x type UARTS, system clock up to 60MHz, Intel or Motorola bus interface, etc.

Sadly it is obsolete...  I noticed XR82C684 is also obsolete. 

  Bill

[Richard Deane]

thanks Alan, the 16C255x  dual port board sounds quite practical. I guess it shouldn't be too hard to hack some of the roms to suit.

Can one use two cards in a system to give a four port solution?

Richard

[Alan Cox]

On Wed, 29 Sept 2021 at 22:06, Richard Deane <rwd...@gmail.com> wrote:

thanks Alan, the 16C255x  dual port board sounds quite practical. I guess it shouldn't be too hard to hack some of the roms to suit.

ROMWBW 3.x should detect it out of the box at 0xA0 I believe

Can one use two cards in a system to give a four port solution?

Yes - it'll jumper at various addresses. You'll need to add some kind of support for more than 2 ports for CP/M as at the CP/M level CP/M 2.2 only has aux and console)

[Richard Deane]

Thanks, lots to keep me busy through the winter months. With my Chromebook I can be totally portable, tinker while queuing for my XMAS turkey. :(

[Hector Peraza]

The OX16C954 is indeed impressive, your board works very nicely, and drivers for CP/M 3 already exist. IIRC, a while ago Tony Nicholson was adding support to UZI280 for the quad-serial board. RSX280 also supports it.

Note that there are still a few quad-serial ICs in production with 128-byte FIFOs (e.g. TL16C750E, although it lacks the '950 extensions - you probably won't need them anyway). But if Plasmo still has a large stockpile of OX16C954 then I don't see what the problem is. Just go for it instead of for two dual-serial boards.

Hector.

[rwd...@gmail.com]

May I be so bold as to ask if you  have a pcb version which uses plcc socket for quad art?

Apart from plcc being easier to solder than smd, on AliExpress the  plcc chip is about £1.50 whereas smd is about £14.

Richard

[Bill Shen]

Richard,
I have 120 OX16C954 in 100pin TQFP on hand so I have not look around, but you are right, OX16C954 in PLCC is much cheaper than TQFP.  Since I need to fix the silk screen on existing design and implement changes suggested by Hector Peraza and I've used up all existing quad serial pc boards, it is time to revise the pcb with TQFP footprint and design new pcb with PLCC footprint.   I have a couple other pcboards to finish up, too, so I better get going!
  Bill

[Richard Deane]

thanks Bill,

I await it's release; have a pack of 5 plcc chips on order  from ali-express

Richard

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[Bill Shen]

Richard,
I did designed a board with PLCC version of OX16C954 and received the board back a couple weeks ago, but the OX16C954 in PLCC package  took a long time to come.  I just received it and try one out.  It appears to work OK.  This is a picture of the assembled board.  I'll start a homepage with design information and assemble instructions.  I've sent a pc board out to you via International Letter mail.  That was a week ago so you may receive it this week.
  Bill

[Richard Deane]

Thank you, yes the new board arrived. I sent a message to you yesterday to thank you privately as well, so should be in one of your email boxes.

It will keep me busy for a week or so getting the parts together.

Richard

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[Bill Shen]

Richard,

I've found your email.  I appreciate the challenge which has spurred me to look into the availability of PLCC version ($5.30 at UTSource) resulting in a hobby-friendly through-hole design that can be used by Z80, Z280, 6502 and 680x0 family of processors.   This part is fast, able to handle clock up to 60MHz with very capable fractional divisor baud generator that can generate serial clock very close to the standard baud regardless of the clock frequency.  The very deep FIFO allows slow processor to handle fast incoming data without hardware handshakes.  All in all it is a very capable 4-channel serial device well suited for many retro projects.

I've started a homepage for PLCC version of OX16C954.  It is a place holder right now while I working on the various documentations. 

https://www.retrobrewcomputers.org/doku.php?id=builderpages:plasmo:quadserplcc

  Bill