A Guide to Pic Microcontroller Paging

Re:A Guide to Pic Microcontroller Paging by indigo945 on Saturday June 13, 2020 @05:19PM (#23512828)

    Technically, the second block of code is not 100% equivalent.
    Why? Well, it uses more instructions (so more memory and
    also takes longer to execute) but it also sets ALL bits of
    the Program Counter, not just the ones that a goto or call
    can.

    We could use the second block of code to goto to a correct
    page, but it would be annoying to use in practice because it
    would mangle the W register.

Does the code even work at all? I don't know anything about PIC microcontrollers, but I would have expected that writing to PCLACH would cause a jump immediately, meaning that the write to the low bits in PCL would never even happen.

[ Parent | on HN ]

Re:A Guide to Pic Microcontroller Paging by roamingryan on Saturday June 13, 2020 @08:10PM (#23513979)

PCLATH stands for Program Counter LATch High (byte).

In this case latch refers to the digital design technique where you have a register that holds bit(s) until some other event happens. The event in this case is a write to PCL. Once the event occurs, PCLATH is transferred to PCH synchronously/atomically with the write to PCL.

[ Parent | on HN ]

Re:A Guide to Pic Microcontroller Paging by Jetroid on Sunday June 14, 2020 @12:20PM (#23518920)

We can write to PCLATH without causing a jump. PCLATH is only read when we goto somewhere, or call a routine, or write to PCL.

[ Parent | on HN ]

Re:A Guide to Pic Microcontroller Paging by grantla on Saturday June 13, 2020 @07:13PM (#23513658)

PCLATH is not actually the program counter; the real PC is only updated at GOTO/CALL time, and then PCLATH will be copied over.

[ Parent | on HN ]