HCS360_11 MICROCHIP [Microchip Technology], HCS360_11 Datasheet - Page 13

• Manufacturer Part Number: HCS360_11
• Manufacturer: MICROCHIP [Microchip Technology]

5.0
5.1
Code word completion is an automatic feature that
ensures that the entire code word is transmitted, even
if the button is released before the transmission is com-
plete and that a minimum of two words are completed.
The HCS360 encoder powers itself up when a button is
pushed and powers itself down after two complete
words are transmitted if the user has already released
the button. If the button is held down beyond the time
for one transmission, then multiple transmissions will
result. If another button is activated during a
transmission, the active transmission will be aborted
and the new code will be generated using the new
button information.
5.2
Federal Communications Commission (FCC) part 15
rules specify the limits on fundamental power and
harmonics that can be transmitted. Power is calculated
on the worst case average power transmitted in a 100
ms window. It is therefore advantageous to minimize
the duty cycle of the transmitted word. This can be
achieved by minimizing the duty cycle of the individual
bits or by extending the guard time between transmis-
sions. Long guard time (LNGRD) is used for reducing
the average power of a transmission. This is a select-
able feature. Using the LNGRD allows the user to
transmit a higher amplitude transmission if the
transmission time per 100 ms is shorter. The FCC puts
constraints on the average power that can be
transmitted by a device, and LNGRD effectively
prevents continuous transmission by only allowing the
transmission of every second word. This reduces the
average power transmitted and hence, assists in FCC
approval of a transmitter device.
© 2011 Microchip Technology Inc.
SPECIAL FEATURES
Code Word Completion
Long Guard Time
5.3
The CRC bits are calculated on the 65 previously trans-
mitted bits. The CRC bits can be used by the receiver
to check the data integrity before processing starts. The
CRC can detect all single bit and 66% of double bit
errors. The CRC is computed as follows:
EQUATION 5-1:
and
with
and
Di
.
Note: The CRC may be wrong when the battery
n
the nth transmission bit 0 ≤ n ≤ 64
CRC 0 [ ]
rect, recalculate for the opposite value of
V
Work around: If the CRC calculation is incor-
CRC (Cycle Redundancy Check)
Bits
voltage is around either of the V
points. This may happen because V
sampled twice each transmission, once for
the CRC calculation (PWM is low) and once
when V
V
sion which could lead to a different value for
V
and the transmission
LOW
DD
LOW
CRC 1 [ ]
n
tends to move slightly during a transmis-
.
+
being used for the CRC calculation
1
LOW
=
CRC 1 0
n
(
+
CRC 0 [ ]
is transmitted (PWM is high).
CRC Calculation
1
[
=
,
CRC 0 [ ]
]
n
0
∧
=
Di
HCS360
0
n
n
DS40152F-page 13
)
∧
∧
Di
CRC 1 [ ]
n
LOW
LOW
n
trip
is