CIRCUIT DESCRIPTION

AUDIO/LOGIC DESCRIPTION (ALL MODELS)
3.3 AUDIO/LOGIC BOARD DIGITAL CIRCUIT

3.3.1 MICROCONTROLLER (U101)

General

The control logic is based on an MC68HC11F1 eight-bit microcontroller (U101). This device has an internal 1K-byte static RAM and 512-byte EEPROM but no internal ROM or EEPROM. Therefore, all program memory is contained in the external flash memory device (U108). In addition, the microcon- troller has several general purpose input and output pins, an eight-channel A/D converter, and synchronous (SPI) and asynchronous (SCI) serial ports. The A/D converter port allows analog signals to be monitored such as the power amplifier temperature, RSSI signal, and vehicle battery voltage.

Separate buses are used for data and memory addressing. The data bus consists of D0-D7, and the address bus consists of A0-A15. The operating speed of the microcontroller is set by crystal Y100. The 9.38 MHz frequency of this crystal is divided by an internal divider to produce a lower internal operating frequency.

Memory

The operating program and most of the personality information used by the microcontroller is stored in 128K x 8 Flash EPROM U108. The use of a Flash memory device allows the program to be conveniently updated using the standard programming setup and special Flash programming software. This eliminates the need to replace the microcontroller or a memory device such as an EPROM. To reprogram the Flash device, the microcontroller is placed in a special bootstrap mode by turning power on with the MODA/ MODB inputs pulled low. This is done by the RPI by applying 20 volts to the PTT pin of the microphone jack.

Radio tuning information is stored in the 512- byte EEPROM in microcontroller U101. External 4K x 8 EEPROM U102 is used in high tier and data models to store additional personality information. An EEPROM can be programmed many times, does not require a constant power supply, and retains data indefinitely.

Temporary data storage is provided by an internal 1K x 8 RAM in microcontroller U101 and by external 8K x 8 RAM U107. These devices are used as a “scratchpad” during program execution.

Reset

The microcontroller resets when power is turned on and also when the 5-volt supply drops below the normal range. Reset clears several internal registers and restarts the operating program. This prevents improper operation which may result during low - voltage conditions.

The microcontroller resets itself automatically for 4064 clock cycles when power is applied to the VCC input. Low-voltage reset is triggered by low-voltage sensor U100. When the 5-volt supply drops to approximately 4.25 volts, the RESET output goes low. This resets the microcontroller and also inhibits operation for as long as it is low. The microcontroller also has internal reset circuits which trigger reset if problems occur with the clock signal, illegal op codes, or the watchdog timer circuit.

Reset is also triggered when the transceiver is Flash programmed. A low pulse is created by C363 and R421 when the MODA/MODB inputs of the microcontroller are pulled low to initiate this program- ming. This automatically places the microcontroller in the flash programming mode. However, reset does not occur when flash programming is complete, so power must be turned off and then on again to resume normal operation.

Data Bus

Abi-directional data bus consisting of D0-D7 is used to transfer data in and out of the microcontroller. It is used to transfer parallel data in and out of memory chips U107 (high tier only) and U108, and also program latches U110-U112. The logic level on the R/W pin determines the direction of data on the data bus. If it is high, data is read into U101, and if it is low, data is written out. The E output goes high to indicate when data on the data bus is valid or when an external device can place data on the data bus.

 

February 2001

3-4

Part No. 001-9800-001