Acorn 6502 Second Processor

This is my Acorn 6502 Second Processor, it comes with 64KB of RAM of which around 44KB is available to programs. Depending on the version of BASIC installed in the BBC Micro, either the highest available 16KB is used to store the HIBASIC ROM in the Second Processors memory, or where the standard version of BASIC is loaded into the memory map the RAM available to programs is split and the ROM occupies the memory map from &8000 - &C000.

When HIBASIC is used, it isn't loaded into the highest 16KB of RAM, as the top 2KB is used for the Second Processor FIFO buffer and the Tube OS respectively so the HIBASIC ROM occupies the memory locations of &B800 - &F800. 

When the 6502 Second Processor is enabled, the 32KB of memory in the BBC Micro is then given over to screen memory and any I/O functions. The processor in the BBC Micro takes on all of the processing for the I/O functions too. This frees the 6502 Second Processor to concentrate on running the application without hindrance.

The Acorn 6502 Second Processor

Change/Repair History

When I acquired this Second Processor, it was in a reasonably poor state being very dirty and requiring some soldering. It was working and as you can see from the photos, it turned out to be quite a nice example once cleaned up serviced.

At some point in the Second Processors history, the connecting cable had been replaced with a 40 way IDE cable. As you can see from the shot below, the middle IDC connector had been removed.

The TUBE cable had been replaced in the past with an IDE cable

As you can see from the photo below, an IDC transition connector was used however the IDE ribbon cable had not been trimmed.

The IDE cable as it was connected to the Second Processor circuit board

The solder work on the 6502 Second processor was pretty poor on the IDC connector with a lot of excess flux left behind.

Here you can see the solder side of the Second Processor

Here's a detailed shot of all that excess flux. The board generally looks messy.

Here's a detailed shot of the previous owners solder work

Here we have a new shot of the new IDC transition connector and ribbon cable in place.

This shot shows the 6502 second processor with a new IDC transition connector soldered in place

Here, the board has been refitted into the 6502 second processor case, you can see the newly fitted ribbon cable has been correctly and neatly trimmed and we're ready to go!

This shot shows the 6502 Second processor remounted in the case

Translate this site