Pocket ROMulator FAQs

Also see: the main Pocket Romulator page 
See the EFI/ECU FAQ for an overview of working with cars computers
Identify GM chip types on this page

How to keep from frying your Pocket-ROMulator

First, connect a wire from something metal on the back of your computer to the ground of test system circuit board. Second, put on a ground strap connected to the same ground of test system circuit board - only now should you think of touching anything electronic. While emulating with the above mentioned connections, your computers ground, the ground of the test system, and your skin surface will remain at the same voltage. 

EFI users should note that  sliding on car seats generates static that breaks electronic things. You should have a ground wire that connects something metal (like a connector screw) on the back of your computer that goes to an alligator clip that you fasten to the frame of the car.  You should then have a ground strap on that is also connected to the car frame. If you don't wear a ground strap you will lose valuable time and equipment.

How do I connect it if my computer does not have a Serial RS232 (COM port) on it?  

See our  USB to Single RS232 or USB to Dual RS232 adapters. Be warned about other 

Why am I in Limp-back mode?

• The most common issue is having the wrong setting of pull/hard pull/soft -- just click the button to toggle it ( this was added for a design flaw in some GM ECUs). This is a sticky setting: the Pocket-ROMulator will remember it even when you close our software and run third-party software.
• Be sure you are emulating the correct chip type - (GM users should see this page )
• Any extra pins should hang off the pin one end - the end with the notch and the red stripe end of the cable. You may need to stack some extra sockets and trim off extra pins to make things fit right.
• bad software image (for different ECU or wrong file format)
• You tried to load the rom while the ignition was off.
• You forgot to reset the ECU computer (by turning the ignition completely off for a couple of seconds) after loading a new ROM file.
• header plugged in backwards
• Extended connections or a ZIF socket can cause problems on ECUs. Remember the memory bus of the ECU is not designed to run long distances or drive the capacitance of a ZIF socket. Use extenders/adapters/ZIF sockets at your own risk.
• Over hang pins on the pin-one end only. (Pin one is marked with a red stripe on the cable)

When the romulator connects it reports its Firmware version in a box next to the com port selector. If you have firmware version 1.50  or earlier you can contact us to get an updated processor or send in the unit to have it updated.

I've had a couple of reports of problems on fiberglass bodied cars (other cars with a bad spark wire may also generate a noise problem.). Wrapping the short ribbon cable with Aluminum foil is said to be a fix. Be sure to 

Arcade game won't start?

Make sure the rom image is loaded with the correct offset.

Problem and LED not lit?

Some computers (mostly laptops) may need to be plugged in (cigarette adapter) if they have non compliant serial port. There is a specification that a serial port is supposed to meet, but some manufactures cut corners - it would be a reason to return of a computer - false advertising and all. You might be able to work around this by using our USB - to - Serail adapter.

The correct sequence for uploading complete ROMS while plugged into the ECU is as follows:

• The car ignition must be on to power up the CPU.

• Load file to Buffer

• Press Buffer to ROM button

• Turn off the ignition and turn it back on before starting the engine to reset the CPU in order to run the new data. Failure to do this can cause erratic results.

Testing the Pocket-ROMulator

If you have a pocket programmer, you can use it to test the Pocket-ROMulator. After selecting the same device type, load the same test file in both the Pocket-ROMulator and the Pocket programmer. Plug the Pocket-ROMulator header into the pocket programmer socket. Set the Pocket-ROMulator to pull soft. run the verify device - it should pass.

Change log

Nerd stuff - Serial Commands for the Pocket-ROMulator protocol

Software needs to set to no flow control and set DTR RTS (active; high voltage).

Version -

1 Byte Long - 'V' (56h) + Checksum (56h).

Return Response is 3 bytes Version # (XXh).(XXh), ID (XXh) + no Checksum.

Current Version is 1.30 with an ID of 1 or 2 (Pocket-ROMulator 1 or 2) , Pocket-ROMulator I 2K-32K. (Don't ask for Firmware update unless you have a real problem)

This command should be issued when your program is first started as this does a Hard Reset of the system. This also let's you know that you have found the Pocket-ROMulator.

Read Block -

Command Format 4 Bytes Long - 'R' (52h) + # of Bytes + 1AF0h(Start Address 2 Bytes) + Checksum.

Return Response is # Bytes of Data from the Rom + Checksum.

Read Block will read a 1-256 Byte Block of data from the starting address, use 0 for 256 bytes.

Note: Access to the Rom by the Host Computer is denied during the Reading of the block of code from the Rom, there is no hidden Read command.

Read Byte -

Command Format 3 Bytes Long - 'r' + 1CD7h(Read Address 2 Bytes)

Return Response is 1 Byte of Data from the Rom.

Read Byte will read a byte of data from address 1CD7h and will return 1 byte.

Write Block (All Versions) -

Command Format 259 Bytes Long - 'W' (57h) + # of Bytes + 1AF0h(Start Address 2 Bytes) + (# Bytes of Data) + Checksum

Return Response is a 'O' (4Fh) + Checksum for OK/Ready after the Bytes are written.

Write a Block will write 1-256 Bytes of data from the starting address. When it is done it will return a 'O' for OK. Use this command for the first down load as it is faster.

Note: This is a hard write, not a hidden or soft write and access to the Rom by the Host Computer is denied during the writing of the block of code to the Rom.

Write Block (Version 1.09 & Up) -

Command Format 259 Bytes Long - 'X' (57h) + # of Bytes + 1AF0h(Start Address 2 Bytes) + (# Bytes of Data) + Checksum

Return Response is a two Byte Checksum of the data written to the Rom (Checksum Lo - Checksum Hi). Checksum is all
bytes added together with no carry, 12 + A5 + 56 + EC = 01F9 Checksum.


Write a Block will write 1-256 Bytes of data from the starting address. When it is done it will return a two Byte
Checksum of the data written to the Rom. Use this command for the first down load as it is faster.

Note: This is a hard write, not a hidden or soft write and access to the Rom by the Host Computer is denied during the writing of the block of code to the Rom.

Hidden Write -

Command Format 4 + # Bytes Long - 'w' (77h) + # of Bytes + 1AF0h(Write Address 2 Bytes) + (# Bytes of Data) + Checksum.

Return Response is a 'O' (4Fh) + Checksum (4Fh) for OK/Ready after the Byte is written.

Hidden Write will write one Byte of data ONLY after the Host Computer has accessed the Rom (On the Fly). This is done during the down time of Rom access and will not interfere with the Host Computers Access to the Rom. If the Byte is not written after 100us a forced write will occur, this assumes the Pocket-ROMulator is not attached to a CPU or the Rom is not being accessed. After the Block of data has been written you will get back a 'O' for OK/Ready.

Status -

Command Format 1 Byte Long - 'S' (53h) + Checksum (53h).

Return Response is 1 byte 'B' (42h) + Checksum (42h) for Busy or 'O' (4Fh) + Checksum (4Fh) for OK/Ready.

Scan function -

Documentation is not complete at this time - A quick overview is that you send a 'P' with a Start and Stop Range address
1000h, 1FFFh and Checksum to start it as follows:

'P'+9000h+9FFFh+Checksum (27256)

You also must set the Upper unused address bits high. You will then get back a 2 byte address when it hits a match within this range. You can receive as much as 5000 hits a second. Sending a 'p' or any command will turn it off. If you send a 'p' it will return a 'p' back to let you know it has been turned off.

Unknown Command -

If an Unknown Command is issued the returned Response will be a '?' (3Fh) + Checksum (3Fh).


Checksum is all bytes added together with no carry, 12 + A5 + 56 + EC = F9 Checksum.

* Multi Unit Address Commands (Hardware Version 1.30 & Up)

Addressing a Unit -

By added a 'A' (41h) + Address (0-FFh) before the Command, multiple Pocket-ROMulators can be address on a single serial port. You must connect all pins in of the Pocket-ROMulators in parallel to the PC serial port. The output pins of all Pocket-ROMulators are Tri-Stated unless data is being sent. The address of each Pocket-ROMulator is stored in the EE at address 1FDh.

** For Help or Any Questions on writing Pocket-ROMulator software Call (913) 422-2094.

For help see this

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