TKOPerformance

I am trying to get a difinitive answer to this question. I have a 1986 IROC Z28 Camaro, engine code F, with auto trans. It is MAF, so I assume that I have the 165 ECM. I am trying to connect my DIY scan tool to the ALDL port in the car. I built the interface box from the plans at the techedge site, and am splicing a weatherpack connector into the ALDL wiring to allow me to interface the scan tool and the ECM. I had problems determining the ALDL pin assignments, because they didn't match up with the diagram for the scan tool. Trickster has answered all my questions about that, but I have one final question. The pins in my ALDL are as follows:

Pin A - ground
Pin B - diagnostic test from ECM
Pin C - air select valve (emissions)
Pin D - SES light
Pin E - data stream
Pin F - torque converter clutch
Pin G - fuel pump relay (12 volts)

My question concerns that data stream from pin E. Is this an 1892 stream or a 160? I believe it should be 1892 (only TBIs use the 160 to my knowledge). I need to be sure to connect it to the right pin out on my scan tool board, and have the option of either the 1892 or 160 position. Any help would be great.

Mangus

'165 uses both 8192 and 160 baud. It floods the port with 160 baud data until it receives a request for 8192 baud info within a 50ms window. Once the request is received successfully by the ECM within the window, 160 baud comm ceases and the port is "chatter free" at which point you can send 8192 baud requests.

Long winded answer to your short question.

TKOPerformance

Okay, that makes sense. Do both the 160 baud and 8192 baud data streams come from the same pin on the ADLDL (in other words, pin E)? Meaning that I only need to have three wires connected to my scan tool to make everyhting work (pins A, B, & E). If this is the case then all that is needed to switch the signal is software related?

I greatly appreciate all the help.

Mangus

In your application, I'm not really sure. On my '89 I think the data is on Pin M...

Most cables have Pin E and Pin M coupled, so it shouldn't really matter. This is what is usually recommended (since this would allow for both scenarios). There are no adverse affects of doing so.

TKOPerformance

Interesting. My ALDL doesn't have a pin M in it, which is what has lead to all of this frustration. What you're saying is that pins E&M are usually connected together anyway?

Inside my interface box the 160 data (pin E) and 8192 data (pin M) go through different parts of the MAX232 IC, and come out at different pins for the serial cable running back to my laptop. My hunch is to just connect pin E to where the pin M is shown to go, because this is the 8192 data input, but I'm not sure that this will work. Any ideas?

BTW, I got the plans for the box at www.techedge.com.au/vehicle/aldl8192/8192hw.htm.

Thanks again for all your help.

Mangus

yes, in most instances that I'm aware of the pins are connected together.

Perhaps someone with more "cable" experience can chime in here and offer you solid advice, but you should be fine as long as one of the data pins (or both) are seeing the max chip.

AFAIK, there is only one *actual* data pin on the DB9.

TKOPerformance

Hmn, that's interesting. The MAX232 is connected to pins 2,3,& 8 of the DB9 on the laptop side. Do you know which pin is the "actual" data pin? Is this data input to the laptop, or data output to the car?

Pin E is shown going through a 22k ohm resistor on it's way to pinout 10 on the MAX232, where is runs through the T2-in part of the chip, and out through the T2-out (pinout 7) and is connected to the CTS, pin 8 of 9 on the DB9. Pin E is supposedly for 160 baud data, per the schematic.

Pin M is shown running through a 1k ohm resistor and into pinout 11 on the MAX232, which is the T1-in part of the chip, which runs out through pinout 14, or T1-out, and then to the RxD, pin 2 of 9 on the DB9. Pin M also runs through a 1N4148 diode before connecting to pinout 12 on the MAX232, R1-out, and runs through the chip to pinout 13, R1-in, and then to TxD, pin 3 of 9 on the DB9. Pin M is supposedly for 8192 data per the schematic.

According the my IC schematic for the MAX232 pinouts 7 & 14 are RS232 outputs, and pinout 13 is an RS232 input. This should mean that my laptop can "see" either the 160 baud data stream, or the 8192 data stream through either pinout 7 or 14. I think that is can then send a request through pinout 13 to the car's ECU to view either 160 baud or 8192 baud data.

My best guess is that I need to join the inputs to the board for pins E & M. Then connect pin E from my ALDL to both these points, allowing for both 160 baud and 8192 baud data to flow from the cars ECU to the laptop. My understanding is that 160 baud data will start, and then it will be the job of the software to request that data be sent in 8192 baud format, and which point the ECU will switch over to 8192.

Craig Moates

On the car side (ALDL connector), there are three connections that need to be made for the 1227165.

1) Ground. This is common, and can/should be tied together between PIN-A, Chassis/battery Gnd, and COM port GND.

2) Data. This is either PIN-M or PIN-E. They are the same. The 1227165 sends both kinds of data (160 & 8192), but on the same pin. If you have PIN-M, connect to that. If you have PIN-E, connect to PIN-E. If you have both, I'd go with M.

3) Diagnostic. This is PIN-B. If you want to log data, then connect a 10k resistor between PIN-B and GND or PIN-A. Without this, the ECM cannot respond to 8192-baud requests. Also, it will not transmit the 160-baud data without the 10k (I don't think).

There's only one data line at the car, remember that and you'll be OK. If you look at the published circuits, you'll see that the bidirectional stuff essentially has a 'buffer' resistor between the circuit receiver (MAX232/Xistor) and the data line, while the circuit 'transmitter' is tied to the data line on the ECM side of that resistor. This is why everything 'echoes' back from the circuit directly (assuming chatter isn't coming in).

On the other hand, the PC's serial port has both transmitter and receiver lines (TX/RX). And of course GND. The other two lines to the PC are used for power supply, where the max current (supplied by setting lines 'high' at the PC) is like 20mA or so.

That's it in a nutshell. Keep an eye on TX vs RX, as it is easy to get mixed up. Transmit from the PC is receive at the circuit, and then once buffered, is transmit again out to the ALDL.

Hope this helps...
-Craig

TKOPerformance

I've got Pin A running to ground, and pin B running to ground through a 10k ohm resistor, just as you specified.

My ALDL does not have an M pin, only an E pin, so that's the one I have to use. I know that this pin can produce either 160 or 8192 baud data.

The reason I'm so confused is that the circuit diagram, from which I built my interface, has a place to tie into pin E and a place to tie into pin M. Consequently I have four wires coming out of the interface, and only three wires from my ALDL.

The part of the circuit dealing with pin M runs through the MAX232 chip to the RxD line in the DB9, so my gut is just to connect pin E from my ALDL to the place where pin M is supposed to go on the interface.

The place where pin E is supposed to go runs through the MAX232 chip to the CTS line from the DB9. Is there any reason why this needs to be connected? Will the interface allow my ECU to just send 8192 data through the place where the M pin is supposed to go, with no requirement to do anything to where the E pin is supposed to go?

Thanks for all your help guys. This stuff is a bit of a bear for me, because I don't have an electronics background. Building the interface was easy, but getting it up and working is another matter!

Craig Moates

Ah yes, that's that funky hybrid interface that's supposed to use the CTS line as the 160 acquisition. Scrap that. Here's what you need to do to modify that circuit to work with DataMaster, WinALDL, etc:

1) Remove R2, disconnect from Pin-10 at the MAX232, and connect PINE to PINM on the schematic.

2) Disconnect the CTS line, and disconnect stuff from the MAX232 Pin-7. This will leave the COM pin 8 disconnected.

Then it should work fine. If you use a MAX232A or a Sipex232A equivalent, then you can use 0.1uF caps. I think ST Micro has a cheap one also that works well. ST232ACN.

TKOPerformance

You're the man Craig! Thanks for all the help. I can't wait to try this sucker out!