HCS301
of unique values. This can be done by programming
OVR0 and OVR1 to 1s at the time of production. The
encoder will automatically clear OVR0 the first time that
the synchronization value wraps from 0xFFFF to
0x0000 and clear OVR1 the second time the counter
wraps. Once cleared, OVR0 and OVR1 cannot be set
again, thereby creating a permanent record of the
counter overflow. This prevents fast cycling of 64K
counter. If the decoder system is programmed to track
the overflow bits, then the effective number of unique
synchronization values can be extended to 196,608.
3.6.4
LOW VOLTAGE TRIP POINT
SELECT
The low voltage trip point select bit is used to tell the
HCS301 what VDD level is being used. This information
will be used by the device to determine when to send the
voltage low signal to the receiver. When this bit is set to
a one, the VDD level is assumed to be operating from a
9V or 12V VDD level. If the bit is set low, then the VDD level
is assumed to be 6.0 volts. Refer to Figure 3-1 for volt-
age trip point.
3.6.3
BAUD RATE SELECT BITS
(BSL0, BSL1)
FIGURE 3-1:
VOLTAGE TRIP POINTS
BY CHARACTERIZATION
BSL0 and BSL1 select the speed of transmission and
the code word blanking. Table 3-3 shows how the bits
are used to select the different baud rates and
Section 5.7 provides detailed explanation in code word
blanking.
Volts (V)
5.5
VLOW
VLOW sel = 0
5.0
Max
Min
4.5
4.0
TABLE 3-3:
BSL1 BSL0
BAUD RATE SELECT
3.5
3.0
Basic Pulse
Element
Code Words
Transmitted
2.5
0
0
1
1
0
1
0
1
400 µs
200 µs
100 µs
100 µs
All
1 out of 2
1 out of 2
1 out of 4
9.0
8.5
8.0
7.5
7.0
VLOW sel = 1
Max
Min
-40 -20
0
20 40 60 80 100
Temp (C)
DS21143B-page 8
2001 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
