Instruction manual

PC24E/25E
Page 19
4.4 Programming the AD7548 Digital to Analog Converter
The PC24E/25E has been designed for straightforward user programming of the four DAC
chips. Being 12 bit DACs they have to be loaded by sending the output data as two bytes to
the appropriate DAC register addresses as shown in figure 10 above. Note that the data must
be right justified and the order of sending the two bytes must be as selected by jumpers J6 to
J9. The source code supplied with the demonstration software may be taken as examples of
programming the DACs.
When the PC24E is operated in the Bipolar mode, writing 0 to the DACs will give a full
POSITIVE output, writing 2047 (7FF hex) will give 0 volts and writing 4095 (FFF hex) will give
full NEGATIVE output. The bipolar transfer function is shown in figure 11 below.
1LSB = 2 x FS/4095
Bipolar
Transfer
Function
FFFh
0 Volts
+ FS (+10V or +2.5V)
- FS (-10V or -2.5V)
000h 7FFh
7FEh
001h
800h
FFEh
O
U
T
P
U
T
V
O
L
T
A
G
E
DIGITAL INPUT CODES
Figure 11 BIPOLAR TRANSFER FUNCTION
When operating the PC24E in the unipolar mode, writing 0 to the DACs will give 0V out and
writing 4095 (FFF hex) will give full scale +2.5 or +10 V.
The PC25E is always unipolar and writing 0 to the DACs will give 4mA out and writing 4095
(FFF hex) will produce 20mA.
The unipolar transfer function is shown in figure 12 below.