Tandy 1400LT Service Manual page 275

TIMERKOUNTER
The program must write a control command to set the counter mode and write the count data that determines the
length of the count operation.
Write Operations
(CS=O, RD=
1,
WR=O)
Address AI A0 Write Target
40H 0 0 Counter 0
41H 0 1 Counter 1
42H 1 0 Counter 2
43H 1
1 Control word register
Control Register Format
m m m
I *
m m
DI
m
S C l SCO RWMl RWMO C
BCD Binaly or BCD
0 Binary Count ( 1 6 Bits)
1
I
BCD Count
(4 Dimid
RWMl RWMO
Read/Wnts Mode
'
Hipher Byte Only
Lower Byte then Hipher
Select Counter or Multiple
Latch
Command
s c 1
sco
0 0 count.,
#
0
0 1 covnter t 1
NOTE.
I l , T s = o . % = o .
W R = 1
12) See Reading the
Counter
1
0
counter
#
2
1
I
1
I
MuIImIe Latch Cornrnmd 121
x.
Don't c a r e
R e a d m r i t e Mode and Count Write
No. of
Writes
Read/Write Mode
Count Register
Higher Byte Lower Byte
Low 1-byte 1 O O H nnH
High 1-byte 1 nnH OOH
Low/High 2-byte 2
nnH
(2nd write)
nnH
(1st write)
nnH
=
Two-digit hexadicimal value
F-6