83C055 Philips Semiconductors, 83C055 Datasheet - Page 14

• Manufacturer Part Number: 83C055
• Description: Microcontrollers for TV and video MTV
• Manufacturer: Philips Semiconductors

Philips Semiconductors
12 SOFTWARE ANALOG-TO-DIGITAL FACILITY
Figure 6 shows the software analog-to-digital facility block diagram. The block includes Special Function Register SAD.
12.1
Table 12 Special Function Register SAD format (address D8H)
Table 13 Description of SAD bits
12.2
Port pins P1.0/ADI0 to P1.2/ADI2 can be alternately
selected as inputs of a linear voltage comparator. The
other input of the comparator is connected to a 4-bit DAC.
This DAC is controlled by bits SAD3 to SAD0 and
produces a reference voltage:
The output of the comparator (HIGH or LOW) can be read
by the program as the MSB of the SAD register i.e. bit VHi.
After writing St = 1, the program should include intervening
instructions totalling at least 6 machine cycles (72 clock
periods or 6 s at 12 MHz), before the instruction that
accesses and tests VHi.
1996 Mar 22
nominally 0.15625 to 4.84375 V in increments of
0.3125 V.
Microcontrollers for TV and video (MTV)
3 to 0
VHi
BIT
7
Special Function Register SAD
7
6
5
4
Software ADC operation
SAD3 to SAD0 4 LSBs of the SAD register.
SYMBOL
CH1
CH1
CH0
6
VHi
St
The comparator output bit; bit addressable.
The channel field controls which pin, if any, is connected to this facility; see Table 14.
The St bit should be written as a logic 1 in order to initiate a voltage comparison.
CH0
5
St
4
14
Table 14 Pin selection: P1.n/ADIn
Note
1. Port 1 has open-drain drivers which will not materially
SAD3
affect an analog voltage as long as any and all pins
used for software analog-to-digital measurement have
corresponding logic 1s in the port register; n = 0, 1, 2.
3
CH1
DESCRIPTION
0
0
1
1
SAD2
2
CH0
0
1
0
1
83C145; 83C845
83C055; 87C055
SAD1
1
Product specification
P1.n/ADIn
P1.0/ADI0
P1.1/ADI1
P1.2/ADI2
none
SAD0
0
(1)