User Manual

PROGRAMMING
3-6
Part No. 001-3422-003
THE A0-WORD
The A0 Word is sent last. the A0 word contains the programming information for the main dividers. The A0
word consists of four divider parameters, NM1, NM2, NM3, and NF described below. After clocking the A0 word,
the STROBE line is held high for approximately 3 ms to place the synthesizer in “speed-up” mode to decrease lock
times.
NF: Fractional-N increment (3 bits, depends on channel selection and FMOD)
NM1: Number of main divide cycles when prescaler modulus = 64 (12 bits)
NM2: Number of main divide cycles when prescaler modulus = 65 (4 bits, PR = 10).
NM3: Number of main divide cycles when modulus = 72 (4 bits, PR = 10)
The Fractional-N increment (NF) is a 3 bit word that is used to program the synthesizer to channels
(frequency steps) that are less then, or a fraction of, the comparison frequency (FCM).
3.2.4 LOCK DETECT
The LOCK detect output from the synthesizer is available for monitoring on J201 pin 7. The LOCK output is
high when the main and auxiliary phase detectors indicate a lock condition. The lock condition is defined as less
then +1 cycle on the reference input to the synthesizer IC. The LOCK detect line should be monitored to verify a
locked condition before transmitting.
EXAMPLE CALCULATION
Program a Band 6 radio to receive at 151.0175 MHz
D-Word Calculation:
NR = 875 (Decimal)
SM = 00
EM = 1
EA = 1
SA = 00
FMOD = 1
LONG = 0
D-Word (Hex) = A3 6B 26