when 128k is not enough

[longpole001]

hi robert

i will still progress on the current 1 cpu for the moment cos i have boards made / even if they are modified , for product testing the last 15k of code space should be enough to get the base requirements going so i can get a product feedback in jan ,

i will make use of the prototype boards for the product in its baseform , and after the feed back ill put that into the design of the 2nd pcb , which will use 2 cpus and break up the tasks as i see them at the moment .

it is a step backwards, in that if i had taken up pic design in C i would not have this as big an issue as i do now and change in platform would not be as painful and this would not be needed

but its been over 20 years since coding in C and i do like basic and PBP , but now i am seeing the many restrictions by the choice.

it is very sad that pbp can not support the larger chips even if it were for just to use the larger code space and use only 8bit fuctions ,
it at least allow some upgrade path using pbp past 128k.

It also seems likely that PBP will not progress in any functionality for some time , apart from adding a few more 8 bit chips in the next year or so ,
also given DT's passing has delayed any further release updates to PBP/ U2 programmer support etc for majority of this year.

Microchip in marketing wisdom have made that choice as well forcing you down the 16bit or 32 bit path just to get a bit more code space.

but this is where i am at so ill just have to make it work


i did not expect this to become as big as it has but to start again on new platform is not practicable given i just want to get it done


cheers

sheldon

[towlerg]

Might I ask, what device are you currently using? and which device would you like to use?

George

[longpole001]

thats intersting question , i expect not , it seem to me more like adding an external flash chip is liuke adding eeprom , great but how o use it more than just storage

[tumbleweed]

When you use the external memory bus of the 87K22, you connect it up to a regular 16-bit parallel flash device and the operation is totally transparent to the program. Program code < 128K uses the internal flash, and addresses above that go to the external memory chip... up to 2M bytes

Assuming that the compiler doesn't have any internal program size limits, there's nothing special you have to do when writing your program... you just end up with a really big hex file.

There are some limits/things to note:

- external memory is slower, so you have to reduce the system clock. The only reference I've found in the 87K22 datasheet is a note that says"Fmax=25MHz in 8-bit external memory mode". Using a 16-bit wide memory may ease this a bit, but there's nothing in the data sheet to back that up.

- you'll likely have to have a bootloader that can program both the internal and external flash devices since the regular ICSP programming tools like the pickit won't work to program the external flash.

- likewise, you can't use the ICD debugging tools, and the MPLAB simulator doesn't support the EMI either.

- there's an errata w/the 87K22 for the EMB. The CE chip select pin won't be extended if you use wait states, so you have to make sure the flash is fast enough to run in a single cycle.