Specifications

2. For the split baud rate mode, J3 must be opened and J4 closed. Timer 1 is used to
generate a square wave on PB7, the frequency of which determines the Full-duplex port
transmitter
baud rate. (Use the values given in Table II for these transmitter baud
rates). With the Shift Register in the free-running output mode,. the receiver clock
frequency
is determined by Timer 2.
-_._---,-------------
'..-..---------------------- ,-_._---------------._-----'-.--------------------
TABLE IVa SIMPLEX SERIAL PORT BAUD RATE SELECTION - 50HZ
BAUD VALUE FOR VIA TIMER 2 LATCH
RATE VALUE
(HEX)
MODE
ERROR-%
-----
9600
79
4F 1 bit/bit
-.33
4800 159 8F 1 bit/bit .28
9600
38
26 2 bits/bit
.91
4800
79
4E 2 bits/bit -.33
2400
159 8F 2 bits/bit
.28
19200 8 8 4 bits/bit .91
9600
18
12 4 bits/bit
.91
7200 25
19 4 bits/bit -.33
4800
38
26 4 bits/bit
.91
3600 52
34
4 bits/bit -.33
2400
79 4E 4 bits/bit
-.33
1800 106 6A 4 bits/bit -.33
1200 159
8F
4 bits/bit
.28
---
TABLE IVb SIMPLEX SERIAL PORT BAUD RATE SELECTION - 60HZ
BAUD
VALUE FOR VIA TIMER 2 LATCH
RATE VALUE
(HEX)
MODE ERROR-%
-
-
.
--
9600
76
4C 1 bit/bit
-.42
4800 153
99 1 bit/bit .23
9600
37
25 2 bits/bit
-.42
4800
76 4C 2 bits/bit
-.42
2400 153
99
2 bits/bit .23
19200
8
09
4 bits/bit
-2.9
9600
17 11
4 bits/bit
2.2
7200 24 18
4 bits/bit
-.42
4800 37 25
4 bits/bit -.42
3600 50 32
4 bits/bit
-.42
2400 76 4C
4 bits/bit
-.42
1800
102
66
4 bits/bit
-.42
1200
153
99
4 bits/bit .23
--
--
---------
--
---
--
Notes for Table IV
1. "Mode" indicates the rumber of bits in the VIA Shift Register which are used to generate
one "bit" of output. The expansion of bits in this manner must be handled in software.
The Simplex Serial Port drivers in the QUARK operating systems use the "4 bits/bit" mode.
2. The actual shift frequency is given by
f
E
/(2N+4),
Megatel
Computer Technologies Toronto, Canada Appendix
Page A-7