Instruction manual

PC24E/25E
Page 20
1LSB=FS/4095
Unipolar
Transfer
Function
FFFh
+ FS (+10V or +2.5V or 20mA)
Zero (0V or 4mA)
000h 7FFh
O
U
T
P
U
T
V
or
I
DIGITAL INPUT CODES
Half Scale
Figure 12 UNIPOLAR TRANSFER FUNCTION
4.4 Programming the 82C53 Counter/Timer
Full details of the 82C53 Counter/Timer and its various programming modes are given in the
appendix. The three counter/timers of the 82C53 can be independently programmed to
operate in any one of six modes, but circuit considerations mean that only mode 2, Rate
Generator or mode 3, Square Wave Generator are useful for generating timed IRQ pulses.
The function of a particular timer/counter is established by writing a control word to the control
register which is located at BA + 0Bhex. This 8 bit word consists of four fields as follows:
D7 D6 D5 D4 D3 D2 D1 D0
Select Counter Read/Load Select Mode BCD or Binary
D0 = 0: Binary counter selected.
= 1: BCD counter selected.
D3,D2,D1 = x 10: Mode 2 Rate Generator selected.
= x 11: Mode 3 Square Wave Generator selected.
D5,D4 = 00: Latch Counter.
= 01: Read/Load LSB
= 10: Read/Load MSB
= 11: Read/Load LSB followed by MSB
D7,D6 = 00: Counter 0 selected.
= 01: Counter 1 selected.
= 10: Counter 2 selected.
= 11: Prohibited combination.
Example 1 To select Counter 1 to Mode 3, loading/reading low order byte followed by
high order byte binary, the controls word is: