HELP: How to Reset a CPU (Microprocessor)

[SaMirakle]

Hi everyone I'm new to the forum and I'm hoping I can get some help here since I work in electronics!

Okay so I'm basically trying to figure out how to use the RESET function on a CPU. The datasheet explains forever about the functions of the microprocessor but doesn't say a darn thing about how to do anything on it really.

I have a circuit that's stuck somehow and I can't seem to get it to "communicate" anymore. I'm trying to see if resetting the CPU registers will help any.

(I can send a link to the datasheet when I get to work)

 

[SaMirakle]

Here's a link to the user's manual:

http://cache.freescale.com/files/microcontrollers/doc/data_sheet/MC683336_376UM_ZIP.zip

I think I actually need help understanding the "Standby RAM Module" section of the user's manual.

Can anyone help clear this up for me? I think the RAM is in standby mode because the battery that provides power to the SRAM went dead and I believe the board won't initiate due to the power loss of the SRAM.

 

[(*steve*)]

It's really hard to give any information because we don't know what board it is you're talking about nor what software is on the device.

 

[SaMirakle]

There isn't software. It's an automotive application. The circuit board is an ECM (Engine Control Module)

 

[(*steve*)]

Well, yes, there is software. But at least we know what the device is.

If it has RAM and if it relies on the data in RAM to operate then there's a chance it needs to have that RAM re -populated with correct values before the device can operate again. Although... If it were me, such values would be in eeprom and not battery backed RAM.

I don't think that resetting the processor is your problem, That happens each time you apply power (presumably).

 

[SaMirakle]

Ohhhh hmm.. But if the values were stored in an eeprom wouldn't it repopulate the SRAM when the battery's been replaced? I've replaced the battery and still nothing.

 

[Sid723]

C4cpu.pdf, page 4-26 tells you about the CPU for this system.

It states:
"4.10.10 Recommended BDM Connection
In order to provide for use of development tools when an MCU is installed in a system,
Motorola recommends that appropriate signal lines be routed to a male Berg connec-
tor or double-row header installed on the circuit board with the MCU, as shown in the
following figure.

Figure 4-12 BDM Connector Pinout"

I couldn't copy and paste the figure here, but the reset is at pin 7 and ground is at pin3 and 5. So, when it is powered on, you should be able to jumper from pin 7 to pin 3 and the CPU should reset itself.

 

[SaMirakle]

Sid,

Thanks for the reply! I tried that and although it may have reset the CPU I wouldn't have known since the results were the same. I'm still not getting any communication from the ECM. Seems as if the boot code has been lost or isn't available since the SRAM had lost power for quite a while.

I bought a BDM programmer so I'll see what I can do with it when it gets shipped to my work.