Technical Manual
Table Of Contents
- Wireless Sensor Interface A720 (addIT™)
- 1. About the A720
- 2. Hardware
- 4. Software
- 4.1. AMOS
- 4.2. Mode Check
- 4.3. A/D Task
- 4.4. The Terminal Task
- 4.5. The Radio Interface Task
- 4.5.1. Digital Squelch
- 4.5.2. Modulation Technique Used
- 4.5.3. Generic Format of a Radio Frame
- 4.5.4. Data Frames
- 4.5.5. Frame Types
- 4.5.5.1. Request
- 4.5.5.2. Broadcast Answer
- 4.5.5.3. Set I/O Request
- 4.5.5.4. Read I/O Answer
- 4.5.5.5. Broadcast Request
- 4.5.5.6. Ping
- 4.5.5.7. Pong
- 4.5.5.8. Memory Dump Request
- 4.5.5.9. Memory Dump Answer
- 4.5.5.10. Data
- 4.5.5.11. Set ID
- 4.5.5.12. Set Slot Time and Sample Rate
- 4.5.5.13. Set Frequency
- 4.5.5.14. Set Battery Charge Levels
- 4.5.5.15. Set Pulse Counters Parameters
- 4.5.5.16. General Acknowledge
10
Wireless Sensor Interface A720 (addIT™)
2.3. The Microcontroller and the Power Management Sections
The operation of the whole unit is under the control of U9, a PIC16C77L microcon-
troller. It is a powerful chip exhibiting an extreme low power consumption. Its main
jobs are:
• Controls the radio unit;
• Implements the modem functionality;
• Assembles the radio frames and waits for requests from a remote;
• Performs the sampling of the sensor inputs and the A/D conversion;
• Stores the values in a local FIFO; manages the FIFO;
• Implements the pulse counter function;
• Increments the Real-time clock;
• Assures the power management;
• Implements a serial Command Line Interface (CLI).
Note: For more details on some of these functions, see also the chapter “Software” on page 34.
The chip operates at its maximum speed, in this case 4 MHz (the “L” version) and
uses a crystal (X1). The real time clock is implemented by means of a 32.768 kHz crys-
tal (X3) connected on the internal TIMER1.
The radio unit is controlled via the SPI bus on one hand (to set the PLL chip param-
eters) and via the switches Q8 (for receive) and Q5/Q7 (transmit). As already men-
tioned, the modem is implemented in software: the output signal is available on RB1
(
TXDI
), while the receiver output is fed on the RB0/INT pin (
RXDO
).
The A/D subsystem is used to sample the inputs (AN0 to AN5); the 7th analog input
is used for on-board measurements (local battery, internal temperature and RSSI sig-
nal, switched by means of the analog switches U6 and U7); a stable 2.5 Volt reference
supplied by U4 is applied to the RA3/AN3/Vref pin. The reference is powered by
the microcontroller only when sampling the A/D inputs. The external sensors are
powered through U13.
The sampled input values are stored in a FIFO built with a serial EEPROM chip, U5.
These values may be retrieved when a pertinent request is received over radio, or
over the serial line. Additional configuration parameters are stored in the EEPROM,
e.g. the serial number of the device, the operating frequency, etc.
The pulse counter functionality is implemented by means of the two inputs RB6 and
RB7, based on the
interrupt on change
feature implemented in the PIC16C7x series of
microcontrollers.
The power management controls the charge/discharge of the battery (via Q9 and
U11), senses the misery levels and switches off the unit in order to protect the battery
(again U11). In addition, the software senses a storage condition, where no activities