User manual

MCP2030 Bidirectional Communication Demo Kit User’s Guide
© 2006 Microchip Technology Inc. DS51637A-page 15
strength. This current output is fed into a resistor and the voltage across the resistor is
fed into the MCP3421 ADC input pin. The converted16-bit ADC output is then fed into
the MCU.
The function of the MCP2030 is controlled by its configuration register settings. Highly
intelligent signal detection and response (bidirectional communications) is possible by
utilizing the MCP2030 configuration register settings. The user can easily change or
modify the included firmware for different settings of the MCP2030 configuration
registers for their own applications.
3.3.4 UHF Transmitter (433.92 MHz)
A 433.92 MHz UHF transmitter is used to transmit the Transponder Demo Board data
to the Base Station Demo Board. The UHF transmitter is based on a surface acoustic
wave (SAW) resonator. The transmitter is turned on during the high duration of the data
and off during the low duration of the bit data.
3.3.5 Analog-to-Digital Converter (MCP3421)
The Transponder Demo Board uses an MCP3421 ADC to convert the analog RSSI
output of the MCP2030 to digital data. The MCP3421 is a delta-sigma analog-to-digital
converter with 12, 14, 16, and 18 bit mode options. In this demo board, the converter
is configured for the 16 bit and one-shot mode. When the transponder is powered-up,
the MCU sends an I
2
C write command to the MCP3421 for one-shot mode and 16 bit
conversion. After one conversion, the device stays in a low power standby mode.
During this mode, the device draws only about 1 µA. When the MCP2030 analog
front-end device receives a valid Base Station command, then the MCU sends an I
2
C
read command to the MCP3421 ADC for the analog-to-digital data conversion. At this
moment, the Base Station Demo Board transmits a continuous LF signal for about
50 ms allowing the MCP2030 to collect the RSSI values. The RSSI voltage across the
RSSI load resistor is fed into the MCP3421 input pin. After the MCU sends the I
2
C read
command, it is waiting for the MCP3421 to complete the conversion by checking the
RDY
bit of the MCP3421 output. In typical operation, it takes about 50 ms to complete
a 16 bit conversion. See Figure 2-2 and Figure 2-3 for more information on the ADC
operation.
TABLE 3-1: PIC16F636 I/O CONNECTIONS
Note: The design and layout of this transmitter is not sufficient to ensure
compliance with EC or FCC regulations.
PORT Pin Function Notes
Port A
RA0 Switch 4 ICSP™ Data
RA1 ICSP Clock
RA2 Switch 3
RA3 ICSP MCLR
RA4 LFDATA Input from MCP2030, SPI SDIO for MCP2030
RA5 SPI SCLK Output for MCP2030
Port C
RC0 RF Active LED
RC1 SPI CS
output for MCP2030
RC2 I
2
C SDA for MCP3421
RC3 I
2
C SCL for MCP3421
RC4 Valid LFDATA Input Indicator LED
RC5 RF Data Out