On Feb 11, 2017, at 4:00 PM, Paul Berger <
phb.hfx@...> wrote:
You understand
that there are two 1K word windows into the ROM and the
bank selection is done by write to the area occupied by
the base page ROM, I think my writeup included with the
package gives a good description of how it works.
Yes. At the moment, I’m looking at the code in bank
0 that appears to be associated with bank selection of the other
banks. There are two instructions that my disassembler flagged
as invalid bit patterns. They are at (octal) word addresses
30272 (pattern 070113) and 30313 (pattern 070117). These do not
match any instructions described in the 9825A patent, nor in the
9835 Assembly Language manual (the 9835 CPU is a superset of the
9825 CPU). The instruction at 30272 happens immediately after a
dir (disable interrupts) instruction, and the one at 30313
immediately before an eir (enable interrupts) instruction. The
rest of the code in this sequence copies blocks of 16 words from
one location to another, I have not yet determined what this
data is.
These apparently invalid instruction bit patterns
do not occur as instructions in the entire contents of the
other 9825T ROMs. I have not yet looked at the contents of
banks 2-7, nor do I have tentative labels or definitions for
base page temporary locations being used.
Notes about the disassembler output.
The second column are word attribute tags derived
from the disassembly process. The ‘r’ indicates ROM, ‘i’ the
word is considered to be an instruction, ‘c’ means a conditional
jump, ‘u’ means unconditional jump.
Symbols in the operand column surrounded by braces
on a line following an instruction are alternative names known
for the operand location. They may or not apply semantically to
that specific instruction. For example, at 30273, the operand
address is the decimal 152 constant in the base page rom. It is
also known, via an equate as b230 (octal 0230).
30256 ri 004177 selbank?
ldb p0 ; perform pre bank select stuff?
{kpa,dpa,ppa,zero}
30257 ri 035742
stb op1
{tvar3,op1e}
30260 ri 004177
ldb p0
{kpa,dpa,ppa,zero}
30261 ri 035767
stb 77767
30262 ri 004077
ldb p58
{b72,colln}
30263 ri 025044
adb stolendsk
30264 ri 035763
stb 77763 ; save address stolen+58
30265 ric 011335
cpa 77335
30266 riu 067315
jmp selbnkjmp ; bank already selected?
30267 ri 031335
sta 77335
30270 ri 022676
ada 31676 ; «(31676) = 055750»
30271 ri 070430
dir
30272 ri 070113
INVALID ; «Unknown instruction, load something
into A?, something else entirely?»
30273 ri 030047
sta p152 ; «write to 0230, select bank 0? Is this an
argument word?»
{b230}
30274 ri 104000
ldb a,i
30275 ri 174510
sbr 9
30276 ri 035762
stb 77762
30277 ri 104000
ldb a,i
30300 ri 174606
sbl 7
30301 ri 174506
sbr 7
30302 ric 044000
isz a
30303 ri 100000
lda a,i
30304 ri 134001
stb b,i
30305 ri 005763
ldb 77763
30306 ri 071417
xfr 16
30307 ri 020127
ada p16
{adr2,b20,ar2a,d16}
30310 ri 024127
adb p16
{adr2,b20,ar2a,d16}
30311 ric 055762
dsz 77762
30312 riu 067306
jmp *-4
30313 ri 070117
INVALID ; «Unknown instruction, store A into
something?»
30314 ri 070420
eir
30315 ri 030041 selbnkjmp sta 00041
; select bank (1)? and jump to code at 077763?
30316 riu 165763
jmp 77763,i
