a E i - Commodore Is Awesome

without
Iso work
nd PC20
thing to
,
sfour
and
t innected
I
6. The
lar con-
B
ferences
Mthat
this
but it
ve also
in f ra me
at 1200
You've
not her
! On a
s using
m LISt
IND/
data.
1
. IV that
uipting
s
.lso be
14. the
e
!rs are
!mory
:uteri
fined
is/4).
t any
(It
you
tate•
rani.
:curs
arge.
Ning
end
of your program. So Beware!
The format for the OPEN statement
is shown below:
OPEN Ifn.dev,sec,CH RS (control
register)+CHR$ (command register)
where:
1fn = logical file number
dev = device (2 for RS232)
sec = secondary address (usually 0)
S - stop bits
0- one
I - two
R (plus 4 only)
0- external clock
1- internal clock
(keep to 1)
Table 2
bit 7 6
S D
D - data bits
DD
00 - 8
01 - 7
10 - 6
II - 5
2400 baud is the maximum speed
that is available on the Commodore
RS232 on the C128. The C64 vvill allow
up to 1200 so this is the maximum
baud rate that I will use in the
PPP
000 Disabled
0010dd
011 Even
101 Mark (I)
III Space (0)
RS232
= see below
= see below
The RS232 interface is device
number two. In order to operate
correctly, the system requires you to
tell it how fast you wish to transfer
data (baud rate) and the format of the
data number of stop bits, number of
data bits, parity). The control
register tells the system the baud
rate, stop bits and data bits as in Table 2.
5 4 3 2
D R B B
B - baud rate
BBBB
0001
0010
0011
0100
0101
0110
01H
1000
1001
1010
1 0
B B
R - Rclock
50
75
1 I()
134.5
150
300
600
1200 (C64 max)
1800
2400 (max)
Plus/4 capable of up to
19200 baud
bit 7 6 5 4 3 2 I 0
P P P D T T R H
P - Parity D - duplex H - handshake
T - Transmit control R - receive control
0 Full
I Half
'VT (Plus/4 only)
00 IRQ Disabled; RTS= I ; TX off
01 IRQ Enabled; RTS=0; TX On
10 IRQ Disabled; RTS=0; TX On
II IRQ Disabled; RTS=0; BRK
Plus/4 users should refer to pages
207-211 of the user manual for further
details on their machine's RS232 interface_
This machine can handle transfer
rates of up to 19200 baud.
Handshake determines how the
interface will operate. We will be using
3-line. X-line is where you are using
control lines as well as the data lines.
examples. If however you have any
problems, try selecting 600 baud
instead.
The command register defines
other interface parameters as follows
H (non PLUS4)
0 3-line
I X-line
R (Plus/4 only)
0 IRQ on
I IRQ off
H (PLUS4)
0 Receiver on
1 Receiver off
Table 3
This makes things a bit complex so we
will stick to 3-line.
Duplex should be set to Full. This
determines how the receive and
transmit will behave.
Parity is a kind of error check.
When data is received, the system
checks it to see if it agrees with the
parity. If not, the parity error bit in the
YOUR COMMODORE january 1987
85
variable ST (status) is set indicating
some sort of error. These bits allow
you to set the type of parity check
required. Of course, both machines
should be set to the same parity. In
most cases, parity is not used and error
checking is done in a different way
(more on this later).
This may seem a little complex but
it isn't really. Lets suppose that we
want to open an RS232 channel to run
at 1200 baud, eight data bits, one stop
bit, no parity. The OPEN statement
would be:
OPEN 2,2,0,CHRS(24)+CH RS(0)
(non Plus/4)
OPEN 2,2,0,CHRS(24)+CHRS(5)
(Plus/4)
and that is that! Simple, eh? In fact, if
you stick to this particular format of
eight data bits and no parity, you can't
really go wrong. Just change the baud
rate to suit.
Incidentally, the Commodore 64
programmers reference Guide tells
you that the command
register character is NOT required.
It's probably safer to leave it in. My
C128 sometimes won't work without
it!
Using PRINT# AND GET# we can
write a fairly simple terminal program
running at 1200 baud. Running this on
two machines (assuming its two
Commodores) you will be able to type
in a message on one keyboard and see
it appear on the other machines display
as well as your own. Figure 7
shows the program while Figure 8
shows a similar program for an IBM
compatible machine running PCDOS
or MSDOS and G BASIC.
Figure 7 Commodore Basic mini
terminal program
10 OPEN 2,2,0,CHRS(24)-1-CHRS(0)
11 REM PL0S4 USERS USE OPEN
2,2,0,CH R$(24)-i-CH R$(5)
20 PRINT "[CLS]"
30 GETI42,AS
40 IF A$"" THEN PRINT AS;
50 GET 13$
60 IF 13S"" THEN PRINT
B$;:PRINT#2,BS:
70 GOTO 30
Figure 8 GM/BASIC mini terminal
program
10 OPEN -
20 COM1: CLS
30 1200, IF LOC( I )=0 THEN 50
40 N,8,1 AS=INPUTS(1,#1);PRINT AS:
-
A
S