DME Electronics

[Tim Polzin]

First of all, many thanks to Chris Bennet and FR Wilks for their help.

Here are a few things uncovered about the 84 to 89 911 Motronic DMEs.

1) They are all 8051 microprocessor based.
2) The 84 to 86 ECUs used imbedded code in the 8051 with the mapping of fuel and ignition contained in the EPROM.
3) The 87 to 89 ECUs have all program and mapping code contained in the EPROM with the internal ROM of the 8051 disabled.
4) The 84 to 86 ECUs can be upgraded to use the code of the 87 to 89 ECUs by replacing the 24 pin EPROM socket (S701) with a 28 pin socket, adding an EPROM with the later code, and adding two jumpers, one to disable the internal memory of the 8051 (B700), and the second to allow addressing the larger EPROM (move jumper B702 to B703).
5) All of the semiconductors on the digital board are standard “off the self devices” with the exception of S700 (the CPU in the 84 to 86 with custom programming) and S100 (which is a custom op-amp which reads the flywheel sensors and generates an angular velocity).

They are:
S702 – 74LS373 Tri-state latch
S703 – ADC0809 8 channel a to d converter
S705 - 74LS02 gate
S890 – LM139 op amp
S704 – CD4049 hex buffer/converter
S100 – Custom flywheel sensor
S700 – 8051 CPU
S701 – EPROM (2716/32/64)

What next?

How different is the late 944 DME from the 911 DME? Are there any hardware differences, or could one be made into another by swapping software?

What about some of the BMW look-a-likes such as the Bosch 0-261-200-059? (These have been going in the $60 range on E-Bay)

The 944 Turbo uses a knock sensor (KLR) in addition to the DME. How much work would it be to incorporate the KLR in a 911 and modify the DME software to retard timing? (See Chris on this one!)

Tim

[Ted Stringer]

Does the 8051 support DMA (direct memory access)? I was just thinking that if it supported DMA, you could rig a SRAM chip to replace the EPROM and add a DMA controler to the memory bus and if you could right to the sram fast enough you could change the fuel and ignition timing on the fly. I don't know about cache for the 8051, but I doubt that its there. Cache would give you a longer time to write the SRAM updates.

I only watched a very small part of the fast and the furious (hated it) but I liked the idea of having diferent maps for diferent applications. One map for the street, another for DE events and mabey a third for auto-x Call me nuts and I know that it is limited also by the mecanicals of the engine, but I think that it would be interesting to try to make a setup that allowed you to change the maps with the engine running. You could have the thing run on a serieal port for updates.

Just a interesting idea for any EEs on the board.

P.S. Please forgive the spelling errors.

[wckrause]

Use a larger external EPROM that contained multiple maps, and then use the uppper address bits of the EPROM to select which map to use. You might get some funny glitches when switching between maps.

There are also devices called ROM Emulators that allow you to load and emulate a ROM from a laptop.

The 8051 is about the most common microcontroller out there. I think I first used one of those around 1983 on a radar altimeter for a cruise missile. No DMA controller, no cache, very limited amount of internal RAM.

[Tim Polzin]

Actually, multiple maps might not be too hard to do. The 87 to 89 digital board will allow addressing up to at least a 27256. With a 27256, and latches on the high address lines, you could create up to 4 individual maps. Should work.

Remember, we are working with 20+ year old technology. This was designed when the Pinto was still a popular car!

Tim

[WydRyd]

Hi Guys,

I am very interested in this post.

Why? Because I am installing an Apexi AVC-R Boost Controller to my turbocharged '89 3.2 Carrera.

I need some technical assistance with respect to pinouts.

The AVC-R EBC requires the folliwing signals:

- Ignition
- Speed Signal
- RPM (or Injector) signal
- Throttle Signal

I need to know which Pins to splice into on the DME.

Can anyone here provide any assistance? Much appreciated!