saa5290 NXP Semiconductors, saa5290 Datasheet - Page 15

• Manufacturer Part Number: saa5290
• Description: Page Economy Teletext/tv Microcontroller
• Manufacturer: NXP Semiconductors

Philips Semiconductors
The 7 least significant bits, TD6 to TD0, extend the HIGH
time of a proportion of the pulses by 0.33 s. If the LSB is
set then 1 in 128 cycles is extended, if bit 1 is set then
1 in 64 cycles is extended, and so on.
S
Up to 3 successive approximation ADCs can be
implemented in software by making use of the on-board
4-bit DAC and multiplexed voltage comparator. The
software ADC uses 3 analog inputs which are multiplexed
with P3.0 to P3.2.
The control of the ADC is achieved using the SAD SFR.
SAD.5 and SAD.6 select one of the three inputs to pass to
the comparator. The other input comes from the DAC
whose input is set by SAD bits 0 to 3. The output of the
comparator is SAD bit 7 and is valid by the next instruction
after starting the comparison by setting SAD.ST to logic 1.
Microcontroller interfacing
The 80C51 CPU communicates with the peripheral
functions using Special Function Registers (SFRs) which
are addressed as RAM locations. The registers in the
teletext decoder appear as normal SFRs in the
microcontroller memory map, but are written to using a
serial bus. This bus is controlled by dedicated hardware
which uses a simple handshake system for software
synchronization. The SFR memory map is given in
Table 10.
February 1995
OFTWARE
One page Economy Teletext/TV
microcontroller
ADC
15
Preliminary specification
SAA5290