Apple-2-SW/tlc-apple2
1
0
Fork 0
mirror of https://github.com/david-schmidt/tlc-apple2.git synced 2024-06-04 20:29:34 +00:00
Code Issues Projects Releases Wiki Activity

Tune for 7-bit ASCII coming from a host

Browse Source 
Signed-off-by: David Schmidt <1110325+david-schmidt@users.noreply.github.com>
This commit is contained in:
David Schmidt 2023-09-26 00:09:46 -04:00
parent 17faf070c8
commit 99addc814e
2 changed files with 16 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

BIN
build/tlcBase.dsk
View File

Binary file not shown.

32
src/bitbangr.asm
View File

@ -31,12 +31,14 @@ start:
jsr PRERR ; Else we got a framing error
printit:
pha
jsr CROUT
pla
jsr PRBYTE
jsr CROUT
jmp start
ora #$80
jsr COUT ; PRBYTE
lda $25
cmp #$17
bne start
lda #$00
sta $25
beq start
done: rts
pb0_recv:
@ -74,11 +76,9 @@ pull_byte:
; Approximately 106.6 ($6B) CPU cycles
clc ; 2
lda PB0 ; 4
bmi :+ ; 2/3
bmi :+ ; 2 if positive, 3 if negative
jmp push_bit ; 3
: sec ; 2 bit was low/negative
; we are now one CPU cycle behind the high case; not going to bother making that up, I don't think
push_bit: ; We now have a bit in the carry
dec bits ; 6
beq byte_complete ; Have we read all 8 bits? Then this bit is the stop bit; leave with carry set
@ -86,17 +86,17 @@ push_bit: ; We now have a bit in the carry
lda ring ; 4
ror ; 2
sta ring ; 4
; $1F cycles to get here
; We are now done with processing that bit; we need to cool our heels for the rest ($6B - $1F = $4C) of the
; $1C/$1D cycles to get here (since center of bit time)
; We are now done with processing that bit; we need to cool our heels for the rest ($6B - $1C = $4F) of the
; bit time in order to get into the middle of the next bit
ldx #$09 ; 2 loop count
ldx #$0A ; 2 loop count
: nop ; 2 \
dex ; 2 |-- 7 * loop count
bne :- ; 3 / final exit of the loop adds 2, branch not taken
; $44 cycles to get here
beq :+ ; 3
: nop ; 2
jmp pull_byte ; 3 Loop around for another bit - we burned $4C cycles
; $48 cycles to get here
nop ; 2
nop ; 2
jmp pull_byte ; 3 Loop around for another bit - we burned $4F cycles
; $6B
byte_complete:
; Carry now holds stop bit (clear/0 indicates framing error, because we end with set/1)