wiring dual bios

modred · Posted: Wed Jun 14, 2006 6:53 pm Post subject: wiring dual bios

here in india, i have not been able to procure a bios savior or similar product. So i set upon the task of making one.

i procured the following parts

1 New Bios chip(similar to one in mobo)
The original Bios from mobo
2 32-Pin PLCC Sockets
1 32-Pin PLCC Adaptor
32-terminal switch

now it would be soldering the wire

Adaptor
|
Switch
| |
PLCC-1 PLCC-2
Bios Bios

Problem is wiring the 32-lines is a elaborate task,
I suspect there may be a simple solution

How is bios savior doing the wiring ?

cp · Posted: Thu Jun 15, 2006 8:06 am Post subject:

32-terminal switch?! how about driving CE# (Chip Enable) to a high level with a pull-up resistor and thus 'deselecting' one of the chips? which leaves us with a 3-terminal switch to GND and much less wirework (piggyback mounting the chips).

modred · Posted: Fri Jun 16, 2006 10:34 am Post subject:

Thanks for replying cp
I greatly appreciate your guidance

I cannot find the CE#(Chip Enable) in the documentation of the Bios Chip, Plz. take a look at page 9
http://www.sst.com/downloads/datasheet/S71161.pdf

NOTE - On my KOB-815e-FSX mobo it is SST 49LF002A /3.3V but the docs available are for SST 49LF008A /3.3V, i guess both are the same except for size 2MB Vs 8MB

I did find OE#(Output Enable) and WE#(Write Enable) pins but the docs say that they are not available in FWH mode

Then there remains ID[3:0](Identification Inputs), docs say these allow multiple parts to be attached on same bus

Hardware details
BIOS Date: 02/23/01
BIOS Type: Award Modular BIOS v6.00PG
BIOS ID: 02/23/2001-KOB-815e-FSX-KOB815eC-00
OEM Sign-On: KOB 815e FSX 02/23/2001
Chipset: Intel 1130 rev 2
Superio: ITE 8712F rev 4 found at port 2Eh
CPU Type: PENTIUM III
Flash Type: SST 49LF002A /3.3V

(SST Web Page)
http://www.sst.com/products.xhtml/serial_flash/49/SST49LF008A

For the pull-up resistor would a 10k ohms be sufficient ?

cp · Posted: Sat Jun 17, 2006 12:11 am Post subject:

okay, i see.

you might use the ID pins and swap the chips' ids around. my first guess would be: ID0 is the BIOS chip.
another approach would be to set IC->high and thus setting the chip to program mode. additionally pull up OE# to make sure the data lines are tri-stated. even if the 'real' bios is now programmed the 2nd chip's data lines are floating and electrically disconnected from the bus.

there's no general value for a pull-up/pull-down resistor but in _most_ cases 10k is a good choice. the internal pull-down resistors on the ID pins are 20k-100k (as stated in the datasheet). so in this case 10k would be the right choice.