gnupic: PIC14e: HIGH directive not setting bit-7
Subject:
PIC14e: HIGH directive not setting bit-7
From:
Richard Hodges ####@####.####
Date:
30 Jul 2013 01:00:04 -0000
Message-Id: <201307291858.56061.richard@hodges.org>
I am writing new code for the 16F1518, and I believe that gpasm is not handling HIGH
correctly for this chip. My datasheet (DS41452C) states on page 19:
"3.1.1.2 Indirect Read with FSR
The program memory can be accessed as data by setting bit 7 of the FSRxH register and
reading the matching INDFx register. The MOVIW instruction will place the lower eight bits
of the addressed word in the W register. Writes to the program memory cannot be performed
via the INDF registers. Instructions that access the program memory via the FSR require
one extra instruction cycle to complete. Example 3-2 demonstrates accessing the program
memory via an FSR.
The HIGH directive will set bit<7> if a label points to a location in program memory."
I _think_ that this access method is only for the "enhanced" 14 bit chips (like the
12f1822 and 12f1501, for example.) But I could be wrong...
This may be the line in question: (line 250 of gpasm/evaluate.c)
case HIGH:
return (evaluate(p->value.unop.p0) >> 8) & 0xff;
I looked at disassembled relocatable code from gplink and I do not see the high bits set
there either.
Here is code to show what happens:
LIST P=PIC16F1518
include p16f1518.inc
testme:
movlw HIGH table
movwf FSR0H
movlw LOW table
movwf FSR0L
table dt 0x5a
end
And here is the disassembly:
> gpdasm -p 16f1518 bad.hex
000000: 3000 movlw 0
000001: 0085 movwf 0x5
000002: 3004 movlw 0x4
000003: 0084 movwf 0x4
000004: 345a retlw 0x5a
I do not know whether the struct pnode has enough information to figure out when to set
the high bit (bit 7) of the result, but I can dig into it if it is not an easy fix for the
main developers.
Thanks!
-Richard
