feipoa, the wiki on x86 memory segmentation might confuse you some more 😁 https://en.wikipedia.org/wiki/X86_memory_segmentation

and yes, you'll need to shadow a 16k range if the rom is 10k.
Software like qemm was able to recuperate the 6k that was unused by the rom, though used by the shadow range for umbs. I think.

I think I've had enough of memory segmentation! Time to move on...

OK, on to the PROM on the 3c515-tx. The manual states that it can take up to 32K PROMs. I assume that is 32 Kilobytes and not kilobits. What I am puzzled by is that the boot ROM DIP-32. If the max is 32 KByte, why would they not use a DIP-28 socket? It got me wondering if the pinout is non-standard. The manual says the part number for the PROM is 3c515TRIROM, but there is very little reference to this online with the exception of some IC part quote places.

I have two of these 3c515-tx cards. I installed a Winbond W27E257-12 EEPRM, which is DIP-28, into the DIP-32 socket on the 3c515-tx with left-most 2 pairs of pins not being used on the socket. Here is a visual of a 3c515-tx: http://ironalbum.pvk13.org/3c515tx-comp_side.jpeg

I removed the Lo-Tech card, installed the 3c515-tx with the W27E257 installed, and booted the computer. I ran 3c515cfg which sees the network card, but the card's connection LED's don't light up. The config utility also cannot detect the network. Is my 3c515tx broken and did the installation of the W27E257 break it, or did the card come broken in the mail? Using my other 3c515-tx card (without the EEPROM installed), the LAN lights turn on and the cfg util can find my network.

EDIT: OK, the boot PROM in the defective 3c515-tx card works! I can set C8000h from within the DOS cfg utility. I then put a "burned" eeprom into my working 3c515-tx and it also works. It was kind of tricky to get the Base Address options to show up in the DOS cfg utility though. The 3Com DOS CFG utility has these options:

C0000h
C4000h
C8000h <<<---- I have selected this one
CC000h
D0000h
D4000h
D8000h
DC000h

[I also noticed how the 3com address convention agrees with the motherboard's convention and not the XTIDE convention]

So I guess that other 3c515-tx card came DOA. It is getting more difficult to get money back from eBay these days unless the hardware has been tested within 30 days. But since the config util detects the card and there just seems to be a send/receive issue over the port, any idea which component may be dead?

feipoa wrote on 2021-08-07, 13:41:

So the table on the Lo-tech website is also wrong? https://www.lo-tech.co.uk/wiki/Lo-tech_8-bit_ … Address_Mapping Or is there another explanation for this? The XTIDE configuration and EEPROM writing software for DOS also indicate these same truncated addresses.

So you are saying that when I select D000 as the address on the ROM card that I should enable ROM shadowing in the MB's BIOS for: D0000-D3FFF and D4000-D7FFF ? I have done so now and it appears to have solved my speed problem! The CF cards now benchmark where they should. I'm left baffled by the truncated address listings.

Hi, address of option ROMs has always, as far as I know, been referenced by segment address rather than linear address, hence C800h for example. Linear address space didn't appear in Intel's instruction set until the 80386 with its protected mode operation.

In terms of ROM shadowing, this is a very important aspect for machines supporting this in relation to achieving good throughput. I've added to Readme to the XTIDE Universal BIOS Binaries Download Centre which includes a link to a page with some information about this and configuring the BIOS as well.

feipoa wrote on 2021-08-08, 14:13:

So I guess that other 3c515-tx card came DOA. It is getting more difficult to get money back from eBay these days unless the hardware has been tested within 30 days. But since the config util detects the card and there just seems to be a send/receive issue over the port, any idea which component may be dead?

Wow, Guess I missed this.
There's only a few things, the connector, the rj45 transformer, and then the chip.
as an example you can check https://github.com/Manawyrm/ISA8019/blob/mast … evA/ISA8019.pdf

weedeewee wrote on 2022-07-16, 11:07:

Wow, Guess I missed this. There's only a few things, the connector, the rj45 transformer, and then the chip. as an example you […]
Show full quote

feipoa wrote on 2021-08-08, 14:13:

So I guess that other 3c515-tx card came DOA. It is getting more difficult to get money back from eBay these days unless the hardware has been tested within 30 days. But since the config util detects the card and there just seems to be a send/receive issue over the port, any idea which component may be dead?

Wow, Guess I missed this.
There's only a few things, the connector, the rj45 transformer, and then the chip.
as an example you can check https://github.com/Manawyrm/ISA8019/blob/mast … evA/ISA8019.pdf

I was eventually able to get the seller to send another one of those 3c515-tx cards. He didn't want the dead card, so it is sitting in my box of dead parts with little motivation to fix it.