Tandy 1000 SL Technical Reference Manual page 46

Address D e s c r i p t i o n
0043/0047
8254-2
T i m e r
IOW- = 0: W r i t e Mode Word
C o n t r o l Word F o r m a t
B i t 0 BCD
0 BCD C o u n t e r ( 4 D e c a d e s )
1 B i n a r y c o u n t e r 1 6 B i t s
B i t s 1-3 Mode S e l e c t i o n
B i t
3
B i t 2 B i t
1
0
0 0
Mode 0
0 0
1
Mode 1
X
1 0 Mode
2
X
1 1 Mode 3
1 0 0 Mode 4
1 0
1
Mode
5
0043/0047
8254-2
Timer
B i t s 4-5:
Read/Load
B i t 5
B i t 4
0 0 C o u n t e r L a t c h i n g O p e r a t i o n
0 1 Read/Load LSB Only
1
0
Read/Load MSB O n l y
1 1 Read/Load LSB F i r s t , Then MSB
B i t s 6-7 S e l e c t C o u n t e r
B i t 7 B i t 6
0 0 S e l e c t C o u n t e r 0
0 1 S e l e c t
C o u n t e r
1
1
0 S e l e c t C o u n t e r
2
< 1 1 I l l e g a l
I O R - =
0: N o - O p e r a t i o n 3 - S t a t e
0048-005F N o t Used
35