Programming The Pacer Clock - Real Time Devices AD1200 User Manual

A/D Blpolar Cocle Table
(+5V; twos complement)
Input Voltage Output Code
+4.998 volts
M S B 0 1 1 1 1 1 1 1 1 1 1 1 L S B
+2.500 volts
0100 0000 0000
0 volts
0000 0000 0000
-.00244 volts
1 1 1 1 1 1 1 1 1 1 1 1
-5.000 volts
1000 0000 0000
1 LSB = 2.44 millivolts
A/D Bipolar Code Tabte
(il 0V; twos complement)
Input Voltage
Output Code
+9.995 volts
M S B 0 1 1 1 1 1 1 1 1 1 1 1 L S B
+5.000 volts 0100 0000 0000
0 volls
0000 0000 0000
-.00488 volts
1 1 1 1 1 1 1 1 1 1 1 1
-10.000 volts
1000 0000 0000
1 LSB = 4.88 millivolts
A/D Unipolar Code Table
(0 to +10V; straight blnary)
Input Voltage
Output Code
+9.99756 volts M S B 1 1 1 1 1 1 1 1 1 1 1 1 L S B
+5.00000 volts
1000 0000 0000
0 volls 0000 0000 0000
1 LSB = 2.44 millivolts
. Programming the Pacer Clock
Two of the tlree l6-bit timer/counters in the 8254 programmable interval timer are cascaded to form the on-
board pacer clock, shown in Figure 4-2. When you want to use tle pacer clock for continuous A,/D conversions, you
must program the clock rate. To find the value you must load ino the clock to produce the desired rate, you fint
have to calculate the value of Divider I (timer/Counter 0) and Divider 2 Climer/Counter 1) shown in rhe diagram.
The formulas for making this calculation are as follows:
Pacer clock frequency = Clock Source Frequency/(Divider
1 x Divider 2)
Divider 1 x Divider 2 = Clock Source Frequency/Pacer
Clock Frequency
To set the pacer clock frequency at 100 kHz using the on-board 8 MHz clock source, this equation becomes:
Divider 1 x Divider 2=8MHzl1OO kHz --> 80 = g y1127100
kHz
4-14