gnupic: Bug in simulation of BSF for in/out ports still present in 0.20.4 :-(
Subject:
Re: Bug in simulation of BSF for in/out ports still present in 0.20.4
:-(
From:
Scott Dattalo ####@####.####
Date:
20 Sep 2000 02:06:23 -0000
Message-Id: <Pine.LNX.4.21.0009192051180.8703-100000@tempest2.blackhat.net>
On Tue, 19 Sep 2000, Wojtek Zabolotny wrote:
> Hi All,
>
> I've downloaded & compiled the GPSIM 0.20.4, and the bug reported in my
> previous post ("Bug in sumlation of BSF instruction in GPSIM?", sorry for
> typing error in subject) is still there. The output of GPSIM session is
> the same, only the GPSIM's version number has changed ;-).
gpsim> 16F877 0x0000 0x2840 goto 0x0040
cycle: 0x01
cycle: 0x02
16F877 0x0040 0x30FF movlw 0xff
wrote: 0xff to W
cycle: 0x03
16F877 0x0041 0x0087 movwf portc
read: 0xff from W
wrote: 0x00 to portc
cycle: 0x04
16F877 0x0042 0x1683 bsf status,5
read: 0x18 from status
wrote: 0x38 to status
cycle: 0x05
16F877 0x0043 0x30C0 movlw 0xc0
wrote: 0xc0 to W
cycle: 0x06
16F877 0x0044 0x0087 movwf trisc
read: 0xc0 from W
wrote: 0x3f to portc
wrote: 0xc0 to trisc
cycle: 0x07
16F877 0x0045 0x1283 bcf status,5
read: 0x38 from status
wrote: 0x18 to status
cycle: 0x08
16F877 0x0046 0x1687 bsf portc,5
read: 0x3f from portc
wrote: 0x3f to portc
cycle: 0x09
16F877 0x0047 0x2847 goto 0x0047
cycle: 0x0a
cycle: 0x0b
As you can see, my version did not change portc to 0x20. Hmm. What inlude file
are you using?
------------
Note that this program has floating inputs. Unlike a real pic device which would
oscillate itself to death, gpsim floating inputs will read as zeroes. So if you
change the tris register to make an I/O an input, this line will float low. Just
so this is clear, let's look at the code:
; The first two lines will make all of the I/O lines high in
; PORTC's output latch. Note that this will not necessarily
; drive the I/O lines high. If the I/O lines are programmed
; as outputs then, yes, it would make them high.
main movlw 0xff
movwf PORTC
;switch to bank1 so that the tris register can be accessed
bsf STATUS,RP0
;Make bits 6 & 7 inputs and the rest of the lines outputs.
;The output lines will now cause the contents of the holding
;latch to be written to the I/O port. So, if PORTC is read
;immediately after writing to TRISC, the lower 6 bits will
;be outputs and set high (because that's what's in the holding
;latch) while the upper two bits which are inputs will be read
;low. This means portc will be 0x3f
movlw b'11000000'
movwf TRISC
;switch back to bank 0
bcf STATUS,RP0
;Bit 5 of portc is now set high. However, since bit 5 is already
;high, this has no effect.
bsf PORTC,5
loop goto loop
end
