APGAC031 Microchip Technology, APGAC031 Datasheet - Page 5

• Manufacturer Part Number: APGAC031
• Description: KIT ACC TIRE PRESSURE MON SYSTEM
• Manufacturer: Microchip Technology
• Type: Automotive, Tire Pressure Monitorr

Specifications of APGAC031

• Frequency: 315MHz
• Processor To Be Evaluated: PIC18F2680
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: APGRD003
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

FIGURE 4:
Details of the LF transmission format and the specific
commands can be found in the Section “LF Com-
mander”.
RF Transmission Format
The encoding method used for this demonstration
system is the 1/3-2/3 PWM format with T
element) time of 400 μs and a bit period of 3xT
1.2 ms.
FIGURE 5:
© 2009 Microchip Technology Inc.
Preamble
Transmitter ID
Pressure
Temperature
Battery
Status
CRC
Logic ‘1’
T
Inductor
L1
E
T
E
T
E
220 pF
C11
LF CIRCUITRY
RF TRANSMISSION
ENCODING METHOD
LF In
10 kΩ
R5
Schottky
D3
Logic ‘0’
T
Bits
E
32
32
16
8
8
8
8
E
T
(basic pulse
E
T
E
CIN-
rfPIC12F675_SSOP
E
or
COUT
GP3
Preamble: The preamble is a series of 31 logic ‘1’ bits
followed by a single logic ‘0’ bit. The preamble allows
the receiver to recognize the RF transmission as a valid
S/TX message. The preamble also allows the receiver
to synchronize to the RF message, thereby compen-
sating for any oscillator inaccuracies within the
transmitter. The system designer may vary the number
of preamble bits based on system requirements. Lon-
ger preamble bit lengths may be appropriate where
receiver quiescent current is an issue. Shorter
preamble bit lengths may be appropriate where S/TX
battery usage is a concern. In either case, it is purely a
trade-off between receiver quiescent current and
battery power consumed by the S/TX device.
Transmitter ID: The 32 transmitter ID bits are used to
uniquely identify each S/TX. A frame of 32 bits ensures
that there is a very low probability that any two S/TXs
will have the same ID.
Pressure: The pressure in kPa is obtained by multiply-
ing the unsigned binary value of this byte by 2.5.
Temperature: The temperature in degrees C is
obtained by subtracting 40 from the unsigned value of
byte 8.
Battery: Bit 7 of this byte indicates the battery
condition. A logic ‘1’ is considered normal while a logic
‘0’ indicates a low battery voltage.
Status: This status byte contains the following informa-
tion:
CRC (2 bytes): Implement according to CCITT
standards.
Bits 0 and 1: Indicate operating state of sensor IC
00 = Initial or Storage mode
01 = Normal mode
10 = Pressure Alert mode
11 = Temperature Alert mode
R3
51 kΩ
LF Out
1000 pF
C9
Schottky
D2
AN238
DS00238C-page 5