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Digital Signal Processing
The DSP chip U2, an ADSP-2185 from Analog Devices, performs the following functions:
(1) receives digitized Doppler signals from the antenna unit
(2) communicates bi-directionally with a serial port device
(3) retrieves operational parameters from the flash EPROM
(4) detects low voltages
(5) filters Doppler signals
(6) checks accuracy against an external reference crystal
(7) determines direction of each target.
U2, Y1, C2, and C3 form a resonant circuit oscillating at 16MHz to supply the clock frequency for the DSP
chip. The DSP chip multiplies this frequency by a factor of four, which sets the instruction rate at 32 millions
of instructions per second (MIPS).
U3, a 1M-bit flash memory chip, holds the software that the DSP chip executes. At power up, the DSP chip
boot loads the software in U3 into internal high-speed program memory where program execution takes place.
The DSP has two serial ports. The first port receives digitized Doppler signals from the A/D converter. The
second port provides bi-directional communication to an external serial device. Pins 31-35 are configured as
serial port 0 (sport0), with pins 35, 34, and 33 receiving the clock, data, and frame synch respectively. Pins 37
to 42 are configured as serial port 1 (sport1); pins 37 and 40 are set to transmit and receive serial data
respectively.
The remaining pins of the DSP chip provide additional I/O control over various parts of the radar unit. DSP
Pins 19, 20, 21, and 24 are the control lines for the flash memory. Resistors R97, R98, and R99 control the
boot-loading source of the software. On DSP Pin 26 (PF4), a logic high enables the antenna. DSP Pin 30
(PF7) controls power to the radar unit, where a logic high maintains power. DSP Pins 74 accomplishes low
voltage detection. (A logic low represents an error condition.) Data lines [D8..D15] receive data from the
flash during the boot-loading process at power up. Address lines A[0..13], including D16-D20, provide flash
addressing (4-Mbit total address space.)
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