Instruction manual

Direct Computer to
Computer Communication
A discovery by Dr. Bohannan: If
your tape recorder has a monitor
hookup, through which you can listen to
whatever
is being recorded, you can
hook up the APPLE directly to the SYM
and reduce the error rate astronomical-
ly! On
our SYM (whose tape interface is
modified as per MICRO's instructions),
we have about a 70% chance of a suc·
cessful load
of our 1500 byte program
with our tape recorder, a Sony. The level
and
tone control settings are extremely
critical as well. When the machines are
hooked up
directly through the monitor
jack of our tape recorder, we have suc·
cess
every time and the level and tone
settings are unimportant. I've also found
that several of my tape recorders work
very well
this way and have the monitor
feature through the earphone jack even
though
it is not marked.
Ending Address
($11 DO-E), Tape 1.0.
Number ($11DF), and the MODE (11 EO)
and start the program at SYMOUT:
($1080). Record the program, play
it into
your SYM, and there you have it'
JKIK OR HS?
J---AND WE'RE ALL DONE
OUTPUTS TH! NEXT KDl LOCATl ON
J---YINo THE NEXT BYTE
CHKL
OUTBTX
CHKH
OUTBTX
Using the Program
It is a good idea to make a SYNC
tape first. The APPLE
output level is
about % of the SYM's output level which
may require changing the volume on
playback from the usual value. Also, the
APPLE does
not have a high-frequency
roll-off
capacitor which the SYM uses,
and as a result, the tone
controls may
need
adjustment. The SYNC tape
enables you to set the controls properly
on
your tape recorder (as outlined in the
SYM manual, Appendix
F). To make a
SYNC tape, load the SYMOUT program
into your APPLE, set the mode by setting
the parameter, MODE (location $11 EO),
to $80 for SYM format or to $00 for KIM
format and begin the program at SYNC:
($1000).
This is an endless loop, so
record a few minutes
of the output
before you hit RESET and use the result·
ant tape to set the level and tone on the
tape recorder when reading
it into the
SYM (see Appendix F in SYM manual).
Once you have the proper level and
tone
settings, down-loading your program is
fairly easy. First, load the SYMOUT pro-
gram. Then, load your executable pro-
gram
into RAM. Next, put in the
parameters: Starting Address
($11 DB-C),
J--- WRITE STARTING ADORESS
I liM ADDiil I 1.oA SAl.
IIIIAD' 21 3811 ,iSR OUTBCX
IIIIB. AD·DCII 1.oA SAM
IIIIB3 211I 3811 JSR OUTBCX
I1B6 2C Elllli BIT KODE
IIIIB9 II IC BP1. oUMPT2
J--- WRITE ENDING ADDRESS +1
IIiBB AD DOli LOA EA1.
IIBE 21 3811 JSR OUTBCX
llCI AD DEli 1.DA EAH
l1C4 21 3811 JSR OUTBCX
J--- START 0. MEMORY DUMP •••
J--- YlRST CHECK If THIS IS' 'THE LAST BYTE OUT
IlIC1 AS Er OUMPT21 1.oA BUfAD1. J---LOAD ADDRESS 0. CURRENT BYTE
l11C9 CO oDII. CMP EAt.
IICC 01 29 BNE DUMPT4 ;---CONPARE TO ENDING ADDRESS
IIiCE AS E8 1.DA BUfADH
1101 CD DEli CMP EAR
1103 011 22 BNE DUMPT4 J---BRAUCH I. WE HAVE MORE TO OUTPUT
J--- YUP, 1.AST BYTE ••• WRITE "IN
liDS A9 2. LOA' '/'
1l107 21 lI711 JSB OOfCTX
J--- VRITE CHECKSUM
110A AD En I 1.oA
111I0021
3BII JSR
lfilEI AD £211 UiA
IIE3 28 3BII JSR
J---VRITE TVO EDT'S
I.E6 A9 '4 1.OAI EOT
I.E8 21 3BII JSR OUTSTX
18ES A9 14 1.oA' EOT
liED 21 3BII JSR OursTX
J--O", NOV VE'RE DONE, SO CLEAN UP & EXIT
III
•• 18 -C1.C ;---INDICATE SUCESS
J--- SKIPPED 1.0TS 0. STU •• , MOST1.Y SYH SPECI.IC
1 •• 1 AI "1 1.DX' SII J---SHUT 0 •• TAPE RECORDER
l1Y3 8E S8C. STX TAP£OY
IIY6 61 RTS
J--- ~EXT IS THE CODE WHICH
IlIIn M II 0UMP1'41 1.oY, $I
un BI £7 1.oA'Y BUYAo1.
llFa 2. 3811 JSR OUTBCX JWRITE IT & UPDATE CHECKSUM
lin: E6 E7 INC BUYADL JBUIlP BUrFER ADDS
II11 DB CS 8ME oUMPT2
11.2 E6 £8 INC BU'ADH JCARRY
11.4 4C C711 JMP DUMPT2 J---eo BACK & SEE 1. WE'RE DONE
;ng to my boss, Dr. Bruce Bohannan. The
APPLE has
almost all of the features of
the typical Microprocessor Development
System, except perhaps, a means
of
communicating with the SSC in ques-
tion.
How can an APPLE talk to a SYM?
Fortunately, both
computers use the
6502 micro-processor chip, so programs
assembled for the APPLE have little or
no trouble running on the SYM or KIM.
Also fortunately, all
of these machines
have a means of reading and writing pro-
grams on audio cassettes. It goes
without saying, of course, that the tape
formats of these machines are totally in-
compatable. So we had to do some
translating; either convince the SYM to
speak APPLE, or convince the APPLE to
speak SYM. Since it's easier to develop
programs on the APPLE [that's why I did
all this in the first place), I decided to
teach my APPLE to speak SYM.
It
turns out that there is another
good reason to teach the APPLE
SYMese. The SYNERTEK people,
who
make the SYM, have been so kind as to
publish listings of ·the SYM monitor in
the back
of their manual. This monitor
listing has routines in it which produce
SYM
or KIM cassette tapes. The result is
that the program is very easily modified
to run on the APPLE. No timers are used
(the APPLE has none), and the serial
data is sent out through a single bit of a
6522
output port. Although the APPLE
doesn't have any 6522s, it does have
several
single bit outputs, and in par-
ticUlar,
it has a single bit output with the
level
adjusted to be used as a cassette
recorder interface. Even though this is
not a 6522 output, under certain condi-
tions it can be thought of as one. The
way
that the APPLE works, any time the
address
of the cassette output port ap-
pears
on the address bus, the cassette
output flip-flop changes state. On the
other hand, in the SYM, we send a par-
ticular bit pattern to an address and
these
bits appear on the output latch.
Basically,
what this means, is that we
can
pretend that the APPLE cassette is
the SYM
cassette output if we write only
to this output when we want to change
the level of the cassette port. With the
APPLE,
it should be noted, there is no
control over the phase of the output
signal, but all of the cassette-read
routines in
question are not sensitive to
phase. Fortunately, through good luck or
the good planning
of the programmers
at SYNERTEK, 90 % of the cassette out-
put code
was written in just this way.
This feature makes
the program a snap
to adapt to the APPLE. Once I had pick-
ed
out the proper pieces of the
SYNERTEK code and figured out what
they had done, I had only to change a
few lines
to obtain the results listed
here. Since I did not write the program, I
won't explain how it works, but I have
heavily commented the
listing for those
readers who are interested.
19:52
MICRO
-- The 6502 Journal
December, 1979