Multiple serial ports

Hardware questions and modifications

Multiple serial ports

Postby jhuyett » Mon Dec 28, 2020 9:03 am

Hello All,
Did search before asking and didn't run across...
Looking to see if there is a way to have more than one serial port. I'd like to be able to keep a mouse connected vs switching peripherals around.

Of course if anyone happened to have a mouse sidecar they'd be willing to part with, that would also solve my problem. I have the Microsoft Green-Eyed mouse w/ 9 pin (looks like serial) which I believe is expecting the Microsoft Bus interface.

Regards
jhuyett
 
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Re: Multiple serial ports

Postby Brutman » Tue Dec 29, 2020 11:49 am

Be careful with the MS mouse - there were serial variants too. If you have the nine pin connector it is probably the bus mouse version, as the serial versions used a 25 pin connector.

On the serial port - there was a modification to the internal modem to basically just turn it into a serial port. Charles Terra also designed a serial port card for that slot - you can find the details at https://www.pcjribm.com/PCJRIBM/JRHardwarePage.htm.

(I'm not sure why Charles doesn't participate here anymore, but either ways his designs were useful.)


Mike
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Re: Multiple serial ports

Postby jhuyett » Tue Dec 29, 2020 12:58 pm

Hello Brutman and thanks for the response.
> there were serial variants too.
Mine is missing pins 1 and 7 which appears to match what I'm seeing with the 9 pin variant of InPort. I bought this long ago for cheap not realizing how difficult it would be to find the sidecar.
Thanks for the info regarding the serial port. The number of surface mounted components put this above my soldering skill level. I'll check in to what's required for the internal modem modification.

Regards
jhuyett
 
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Location: PA, US

Re: Multiple serial ports

Postby Brutman » Tue Dec 29, 2020 1:18 pm

That's definitely a bus mouse.

On the serial port - it seems like an easy enough card to design. The slot is fairly specific, so really it should just be the UART chip and possibly some support chips to handle the voltage difference between TTL and RS232 voltage levels.

The 16550D chips that you can purchase at Jameco cost $6 and have 44 pins:
  • Eight pins for data in/out
  • Three pins for register selection on the UART
  • Three pins for chip select, which is kind of moot for this slot
  • Interrupt pin for signaling the programable interrupt controller
  • Out1 and Out2, which I think are used to disable interrupts from the chip
  • Clock input; You need to use the Jr clock to keep the baud rate divisor compatible with the Jr BIOS
  • A few others

Output pins to the port: DCD, DSR, CTS, DTR, RTS, RI, Data In, Data Out

I'd rather not design it myself but it should not be horrible, and there are plenty of existing designs to steal from. I'd like a second serial port too, but it has not been a burning desire.

Besides Charles' design, are there any other serial port design for the Jr out there?

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Re: Multiple serial ports

Postby Chuckphd53 » Sat Jan 09, 2021 3:04 pm

Hey guys still here... life had interrupted my JR time...

I do have the Jr Modem slot Serial port board...
It gives the Ring Indicator line missing from the back side serial port...
IBM needed another Gate fir,that line, assuming cost savings was the reason for leaving it off..
I also a have the ADD ON schematic for the Ring Ind line on the back port, as there is a free pin, just need to add the chip... then you have full funtionality.

Questions ???
(PCJR/JR-IDE-512DOM,TandyMod,V20-10Chip,BiDir,LPT2,3FlopBrd,
USBEmulator,ZIP100,PS2Keybrd,MouseSysMouse,InternalSwitcherPS)
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