User manual

MCP2030 Bidirectional Communication Demo Kit User’s Guide
DS51637A-page 12 © 2006 Microchip Technology Inc.
3.2.5 125 kHz Low Frequency Command Initiator
The 125 kHz PWM from the PIC18F4680 is power boosted by the MOS FET driver
(TC4422). The PWM square pulse becomes a sine wave as the current passes through
the LC series resonant circuit formed by L1 and C2, C3, and C4 on the Base Station
Demo Board. The current that is passing through the L1 generates a magnetic field.
When this magnetic field transmitted from the Base Station Demo Board is passing
through the Transponder Demo Board’s antenna coil, it produces a voltage. This
voltage is detected by the MCP2030 LF front-end device and the information carried on
the voltage is processed by the PIC16F636 microcontroller on the transponder.
See Recommended Reading for more details of the near-field magnetic coupling
principles.
3.2.6 Power
Power can be supplied through J1 power jack. The voltage should be in the range of
9 - 18 VDC with a current rating greater than 500 mA.
3.2.7 MCU FIRMWARE ALGORITHM
The bidirectional communication method between the Base Station Demo Board and
Transponder Demo Board is shown in Figure 2-2. The Base Station Demo Board sends
an LF command, receives the responses from the Transponder Demo Board, and dis-
plays the received responses on the LCD. The Base Station Demo Board repeats the
transmitting and receiving functions as long as its power supply is connected.
Figure 3-1 shows the LF command data format and waveform. The receiving data for-
mat is shown in Figure 3-5. The MCU firmware for the communication algorithm is
included on the MCP2030 Bidirectional Communication Demo Kit CD ROM.
FIGURE 3-1: Base Station Demo Board LF Command Data Format.
Transmitting Data: LSB First
Wake-Up Filter
2ms
2ms
4ms
AGC Stabilization Time
500 ms
Gap
High Duration
Low Duration
Command Type
32 bit ID+RSSI+Parity Bits
3C+Parity + Stop bit
Waiting for Response
High Duration
Receiving Data: LSB First
(Parity bit per byte)
AGC Stabilization Time
Gap
Wake-Up Filter
= 1100 0011P
= LSB first of 3C (hex)
Command Type (3C)
Stop bit
Continuous LF Field
This allows the Transponder
to sample the RSSI data
+ Continuous LF
+LF turns-on for 50 ms