8051 Non-invasive unbricking

[steveo]

a small project log

for bricked lt1 ecms where the flash chip is still ok, to avoid socketing them as a repair measure, re-flashing without removing the chip seems to be a good way to go. not everyone wants a socket.

kur4o tipped me off a while ago that there's an unused header on the board that's mostly connected to the flash chip.. and doing a bit of ohm-metering this certainly seems to be the case.

my plan is to fabricate a solderless connector for this header and a small harness to go to my programmer, so i can just hook it to an 8051 board and fix a borked flash.

the other possibility i thought of, is modifying a plcc socket to work upside-down and building a small harness to go to my programmer, but i want to use this header just for the fact that it's a bit more of a challenge.

the header seems really ideal, though.

i'm not sure if it's completely pinned out or not, im going to sit down, scrape off all the silicone, and get a proper mapping. will report back with pinouts soon.

one question, does anyone know if ALL of the pins are necessary for programming, or if some can be omitted? (data sheet pic attached)

the only other thing i haven't figured out is the best way to build a connector for it. copper springs seem ideal, kind of like in a standard pc card socket.

[Montecarlodrag]

I have used PLCC sockets for On-Board programming. Custom software has to be written to accomplish that since universal programmers will not work with a soldered chip. All of them had a custom circuit board. It works pretty good, the devices I used in the past saved me a lot of work and I made a lot of money with them
Something like this

[steveo]

Custom software has to be written to accomplish that since universal programmers will not work with a soldered chip.

can you elaborate on that, why wouldn't it work on a soldered chip, and how could that be worked around in software??

[steveo]

pinout of the header (numbered as pictured) to the flash chip:

FLASH PIN, HEADER PIN
1,22?? (VPP)
2,NONE
3,7
4,18
5,13
6,14
7,35
8,20
9,11
10,10
11,9
12,36
13,28
14,27
15,26
16,22(GND?)
17,25
18,29
19,30
20,31
21,32
22,NONE
23,12
24,NONE
25,19
26,33
27,34
28,37
29,8
30,NONE
31,6
32,1

seems like VPP is grounded when not in use? so i need to find the pin that goes to whatever applies vpp voltage?

[Montecarlodrag]

Universal programmers give all kind of errors when you try to program a chip soldered to a board. They are not designed to do that, they need the chip to be placed directly on it to work.
The tools I have used to flash directly on-board chips were custom interfaces with special software.

The header in your picture appear to be some kind of BDM, it may be a better approach.

[kur4o]

VPP comes from small 8 pin chip on black/red side. It is shorted on both sides.
That`s the label on the chip. It is at middle of board.
014
m36av
65422

My first impresion was that these pins were left for connecting the two boards. Later found by accident that most pins goes to flash chip.
I guess the point of this header is for devepment purpose. Looks like as a memcal header, external chip board header, or some special gm private tool to access direct memory addresses for debuging.
I notice that all later style boards, up to 2005 have similar style headers.
I also want to get a hold of one of this memcals with the proprietary software it comes with. It will be real fun.

[Montecarlodrag]

Those pin headers normally are a Jtag or BDM interface, only used for production/development repairs since they give direct access to the CPU and allow flash even without a running OS.