SAA5X9X Datasheet, PDF (13/68 Pages) NXP Semiconductors – Economy teletext and TV microcontrollers

Philips Semiconductors
Economy teletext and TV microcontrollers
Preliminary specification
SAA5x9x family
7.3.7 SOFTWARE ADC
Up to 4 successive approximation ADCs can be
implemented in software by making use of the on-chip 8-bit
DAC and multiplexed voltage comparator. The software
ADC uses 4 analog inputs which are multiplexed with
P3.0 to P3.3.
must be performed at least 1 instruction cycle before the
setting of SAD.ST to ensure comparison is made using the
correct SAD.SAD7 to SAD.SAD4 value.
The output of the comparator is SAD.VHI, and is valid after
1 instruction cycle following the setting of SAD.ST to a
logic 1.
Table 9 ADC input channel selection
CH1
0
0
1
1
CH0
0
1
0
1
INPUT PIN
P3.3/ADC3
P3.0/ADC0
P3.1/ADC1
P3.2/ADC2
The control of the ADC is achieved using the Special
Function Registers SAD and SADB.
SAD.CH1 and SAD.CH0 select one of the four inputs to
pass to the comparator. The other comparator input
comes from the DAC, whose value is set by SAD.SAD7
(MSB) to SAD.SAD4 and SADB.SAD3 to SADB.SAD0
(LSB). The setting of the value SAD.SAD7 to SAD.SAD4
handb_Poo₃k_.,₀halfpage
P3.1
P3.2
MULTIPLEXER
P3.3
ST
C1
1D
VH1
8-BIT DAC
CH1, CH0
REF−
REF+
SAD7 to SAD0
MGL115
Fig.4 SAD block diagram.
1997 Jul 07
13