Table of Contents
Advertisement
This
status
information
from
the printer
can be
tested
by
the
TRS-80
CPU
if
we
connect
it
to
one
of the four inputs
available
on
the
RS-232-C
Interface
(CTS.
DSR,
DC
RI).
A
jumper
wire
from
pin 6
of
the printer
connector (assuming
the standard
DB-25
is
used
on
the printer) to the "status
output"
of the
printer
should be
the
only modification needed.
The
printer
should
now
be ready
to print
if
we
can provide
the
proper software
to interface
with
it.
Before
we
can
actually
output
data,
the printer
and
the
RS-232-C
Interface
must
be
properly
initialized as
to the
baud
rate,
word
length, parity
convention and
stop
bits
required
by
the
printer.
This
is
one
of the
tasks
which
must
be taken
care
of
by
the
driver
software.
The
assembly language
listing
on
pages
27 and 28
provides
Software
to drive
a
DECWRITER.
Lines
1
80 through
440
of
the
listing
comprise
the
initialization
section
of
the driver routine.
This
section
of
code
tests a flag in
memory
to see
if
the Interface has
been
initialized,
and,
if
so,
branches around
the
rest
of
the
initialization
section
and
goes
directly to
the
actual
output
section
of
the
code
(lines
500
through
620).
The
initialization
occurs the
first
time the
driver
program
is
called
by
BASIC
and
a flag
is
set
indicating
this fact.
This section
of
code
is
bypassed on
successive
calls
to
the
driver routine.
Assembly Language
DECWRITER
Driver
Program
88E8
88E9
80EB
7F88
7F80 E5
7F81 C5
7F82 F5
7F83 3A487F
7F86 FE81
7F88 2828
7F8A 3E81
7F8C 32487F
7F8F D3E8
7F11 DBE9
7F13 E6F8
7F15 F684
7F17 32477F
7Fifl
D3EA
7F1C DBE9
7F1E E687
7F28 213F7F
7F23 8668
88180 RESURT
EQU 8E8H
;
AN OUT TO THIS L0C
RESETS
THE
UART,
AN
IN
RERDS
THE RS232 CONTROL BITS
88118 SWITCH
EQU 8E9H
;
RN OUT TO THIS L0C LORDS THE BRUD RATE GENERATOR, RN
IN
RERDS THE SENSE SWITCHES
88128 CNTREG
EQU 8ERH
;
RN OUT TO
THIS LOC LORDS THE URRT CONTROL
REGISTER, RN IN
RERDS THE URRT STATUS
REG.
88138 DTAREG
EQU 8EBH
;
RN OUT TO THIS
LX
LORDS TH URRT XMIT HOLDING
REG.
,
RN
IN
READS THE RECEIVED DATA
88148
ORG 7F88H
;
32512D ORG FOR DRIVER
88158
;
RS232C OUTPUT DRIVER TO BE USED WITH THE LPR1NT COMMAND
IN
LEVEL
II
BRSIC.
88168
,
THE DRIVER
IS
POKED INTO HIGH MEMORY (16K MACHINE) AND THE DEVICE CONTROL BLOCK
88178
;
CHANGED
TO VECTOR THE LPR1NT
COMMAND TO THE RS232C DRIVER WITH A SHORT BASIC
PROGRAM.
88188
IN1T
PUSH HL
;
SAVE
REG.
USED
88198
88208
88218
80228
80238
80248
80258
88268
00278
08280
08298
88380
88310
00328
88330
88340 BRUDST
00358
08368
08378
PUSH BC
PUSH
RF
THIS SECTION
OF
CODE
IS
USED
TO
INITIALIZE THE RS232C INTERFACE TO CORRESPOND TO
THE OPTIONS SPECIFIED BV THE SENSE SWITCHES
IN
THE INTERFACE (BAUD
RATE,
STOP
BITS,
BITS/CHAR.
ETC.
)
LD
A,
(FLAG)
CP 01H
JR
2,
RESTOR
LD
A,
01H
LD
(FLAG), A
OUT (RESURT),
A
IN
A,
(SWITCH)
RND 8F8H
OR 84H
LD (SWT1MG),R
OUT (CNTREG), R
IN
R,
(SWITCH)
RND 87H
LD
H,BDTRBL
LD B,88H
CHECK FLAG TO SEE
IF
URRT AND BRG HRVE BEEN
INIT.
RESTORE
REG.
AND OUTPUT CHRR
IF
SO
SET FLAG TO INICRTE
INIT.
RERD 37DCH TO RESET URRT
READ SENSE SWITHES
LOP OFF LOWER
3
BITS
RESETS
RTS,
RESETS DTR,SETS BRK
IN
HANDSHAKE LATCH
LOAD SWTIMG W/1MAGE
OF
LATCH BITS
LORD URRT W/SWITCH IMRGE
SET BAUD RATE
ACCORDING TO SWITCH SELECTION
LOP OFF UPPER 5 BITS
POINT TO FIRST LOC IN BRUD TBL
ZERO
B
REG
27
Advertisement
Table of Contents
