Ethernet for PCjr {WizNet}

Hardware questions and modifications

Re: Jr Cartridge Ethernet {IDEA}

Postby Shaos » Tue Jan 24, 2017 11:53 pm

Does somebody have signal description/diagrams for modem slot?...
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Re: Jr Cartridge Ethernet {IDEA}

Postby Shaos » Wed Jan 25, 2017 12:08 am

Nevermind, I found it in PCjr Technical Reference book:

Image

Code: Select all
 A1 - D7         B1 - 5V
 A2 - D6         B2 - /MODEM CS
 A3 - D5         B3 - A9
 A4 - GND        B4 - /TXRES
 A5 - D4         B5 - GND
 A6 - D3         B6 - A2
 A7 - D2         B7 - A1
 A8 - GND        B8 - A0
 A9 - D1         B9 - GND
A10 - D0        B10 - /IOR
A11 - MODEM INT B11 - /IOW
A12 - GND       B12 - GND
A13 - BAUD CLK  B13 - /CARD INST
A14 - 5V        B14 - TXRES
A15 - 12V       B15 - 5V

So it's only 4 address lines? I guess reading from internal WizNet 32K memory will be much faster in case of cartridge than modem slot...

P.S. But actually in indirect mode of W5100 chip, when only 2 address lines are used instead of 15, and with help of automatic increment of the address (to avoid setting it for every byte), it may work with similar speed! :roll:
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Re: Jr Cartridge Ethernet {IDEA}

Postby Shaos » Wed Jan 25, 2017 1:46 am

Trixter wrote:
Brutman wrote:For Ethernet I'd love to see something in the modem slot. It has an interrupt line. It has I/O ports. Putting wired Ethernet in there should be easy.


Additionally, no case modifications would be necessary, since the window is wide enough for an RJ11 and will probably take an RJ45 just fine.

You are right - it fits perfectly :)

Image

The only problem - WizNet module will be 90 degree to the vertical board (and upside down) so I should invent some interconnection between them:

Image

In case of indirect mode of W5100 this module (WIZ812MJ for $30) could be almost directly connected to the modem slot, so my interface board will have 3.3V regulator (chip is 3.3V, but all inputs are 5V tolerant), a transistor to convert 3.3V signal back to 5V for interrupt signal, a few resistors and may be a serial EEPROM to store MAC-address (W5100 doesn't remember anything after reset) - so it has to be relatively cheap right away like $50 with WIZ812MJ module or $20 without and bare board will be even cheaper!

P.S. Actually it looks like /CS is shared with floppy controller and A9 should be used to differentiate them:
if A9=0 then it's floppy
if A9=1 then it's modem
so it will be some logic glue as well...
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Re: Jr Cartridge Ethernet {IDEA}

Postby alanh » Wed Jan 25, 2017 7:32 am

Yes, you are correct. ZM52 (ROM) decodes that chip select - asserting it for addresses 0F0h->0FFh (floppy) and 3F8h->3FFh (UART).
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Re: Jr Cartridge Ethernet {IDEA}

Postby Shaos » Wed Jan 25, 2017 12:54 pm

alanh wrote:Yes, you are correct. ZM52 (ROM) decodes that chip select - asserting it for addresses 0F0h->0FFh (floppy) and 3F8h->3FFh (UART).

Ok, thank you for confirmation! Do you know if BIOS (or DOS) is doing something with these ports on initialization if modem card is inserted?

P.S. I found it - BIOS calls subroutine UART with modem base address if card is inserted, so I guess solution is not to ground /CARD INST to prevent this call, right?...

Image
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Re: Jr Cartridge Ethernet {IDEA}

Postby alanh » Wed Jan 25, 2017 3:55 pm

That would make sense
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Re: Jr Cartridge Ethernet {IDEA}

Postby Shaos » Wed Jan 25, 2017 5:20 pm

Also I didn't find anything else on schematics for what this signal (/CARD INST) is used in hardware except for going to port C to be read by BIOS on startup, so my assumption is all other lines in modem slot will keep working even if /CARD INST is not grounded
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Re: Jr Cartridge Ethernet {IDEA}

Postby Brutman » Fri Jan 27, 2017 10:24 am

Even if the number of ports is too limited, we can do something in the packet driver to enable multiplexing of addresses similar to the way older graphics cards (EGA?) have you select a register before writing to it. I wouldn't be too concerned about that; we'd just try to make sure the ports requiring the latching are less used than the performance path ports.

People have stuck other cards in the modem slot before; a SCSI controller in particular. I think that card select line is just really there for the benefit of the BIOS. If I stick a logic probe on any of the pins I'm sure I can make them wiggle without card select engaged.
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Re: Jr Cartridge Ethernet {IDEA}

Postby Shaos » Fri Jan 27, 2017 11:08 am

Yes, for now I think WizNet module with W5100 chip onboard looks surprisingly well suitable for this modem slot :)
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Re: Jr Cartridge Ethernet {IDEA}

Postby OldComputerGuy » Mon Mar 06, 2017 6:56 am

Brutman wrote:
For Ethernet I'd love to see something in the modem slot. It has an interrupt line. It has I/O ports. Putting wired Ethernet in there should be easy. Wired Ethernet isn't as cool as the jrIDE based emulated hard drive/wifi/Linux co-processor that Alan isn't work on, but it also doesn't require a jrIDE and it's really simple in comparison.



Why not wi-fi?
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