1/2R A built-in divided by 2 circuit which provides an output of half the 10.240 MHz Reference
Oscillator frequency, or 5.12 MHz. If used, it normally connects to a tripler circuit to provide a 15.360
MHz signal(5.12 MHz x 3) which can be used for loop mixing with the 16 MHz VCO. This mixing
provides a low-frequency signal input or downmix to the Programmable Divider.
RB Buffered output of the 10.240 MHz Reference Oscillator. Thig signal if present can be used for
mixing with the 10.695 MHz receiver first IF or mixing with the 16 MHz VCO during TX mode to
provide the 455 kHz second IF (RX) or the direct on-channel TX frequency.
F
IN
Input to the Programmable Divider which is coming from the output of the VCO. Sometimes called
''PI'' (Programmable Input) or ''DI'' (Divider Input) by some manufacturers. This is the actual downmix
signal or direct VCO signal in the faster chips which will be compared to the Reference Divider's
output in the Phase Detector. It is the change in this signal's frequency which forces the Phase
Detector and VCO to correct until the loop locks.
DO Phase Detector output. Sometimes called "PO'' or ''PD
OUT
" (Phase Output) or "EO" (Error Output)
by some manufacturers. This is the output which results from comparing RI and F
IN
. If the two inputs
don't match exactly, this circuit sends a DC correction output to the Loop Filter/VCO until the loop
corrects itself and locks up.
LD Lock Detector. Sometimes called "LM" (Lock Monitor) by some manufacturers.This is a second
output of the Phase Detector which is used to kill the transmitter (and sometimes the receiver) if the
loop is not locked and operating correctly. Some chips have more than one Lock Detector pin and thus
you'll sometimes see''LD1'' and "LD2" on the specs. When two Lock Detectorg are used, their normal
outputs are usually opposite logicstates; i.e., one LD ig normally ''1'' and the other is normally ''0''.This
is a convenient design feature which allows the manufacturer some flexibility because he can have a
choice ofinhibiting circuits; some work with LOW outputs,some work with HIGH outputs. Some rigg
use both LD pins in their circuits.
MC Misprogram Code Detector. The same idea as the Lock Detector, this is found in the newer ROM
chips. If you try to force an illegal program code on the chip, this pin is activated and will kill the
transmitter, receiver, or in some cases, call up Ch.9 or Ch.19 instead.
T/R Transmit/Receive switch. This is used to provide the 455 kHz offset for the receiver's second IF
stage in dual-conversion AM or FM rigs. Pressing the mike button changes this pin's logic state to its
opposite state from the RX Mode.This shifts the ROM controlling the Programmable Divider, and in
some chips also shifts the output of the Reference Divider from standard 5 kHz steps to 2.5 kHz steps.
The T/R shift is the reason you`ll see two different sets of N-Codes and VCO frequencies in a rig' s
service manual.
NOTE: Some manufacturers' chip spec sheets show a bar (-) above some pin functions, such as LM,
T/R, etc. This bar is a digital logic symbol which indicates what state (''1'' or ''0'') th'at pin is in when
activated. For example, theT/R with the bar notation means that the pin is normally HIGH ("1") in the
Receive Mode and normally LOW ("0") in the Transmit Mode. /LM means the Lock Monitor is "active
LOW". , i.e., it is normally HIGH but goes LOW if the loop is unlocked.
FS Frequency Select. This is a feature of some chips which allows them to synthesize frequencies in
either 10 kHz CB steps, or 5 kHz steps. Remember, some older chips such as the PLLO2A were
intended for other uses besides CB, such as VHF marine radios, aircraft radios, etc., where 5 kHz
channel spacing is common. In addition, this feature often makes it easier to synthesize SSB
frequencies as well as AM/FM although the feature hasn't been used much for this. Depending upon
whether the chip has an internal pull-up or pull-down resistor here, it is generally connected to produce
10 kHz CB spacings in the older chips. The newer chips having a T/R shift must use the 5 kHz spacing
when the T/R pin is also used. IMPORTANT: You can't use this function to get 5 kHz channel
spacings, because the Programmable divider must also change to match the spacing.
AI and AO Active Loop Filter Amplifier input and output. This circuit if present is used to smooth out
the digital waveform coming from the Phase Detector, before it's applied to the VCO (See text.) This
filter is found in the newer CB-only chips. The older chips (Eg, PLL02A) require external passive filters
using capacitors and resistors. In many rigs you'll find that these pins are connected either directly or
through a resistor so that they are placed in series betw een the Phase Detector output pin and the
VCO input.
FIL Active filter. W e're using this designation in certain very old chips when the exact spec sheets are
not available but it's known from studying the chip's wiring in the rig that the pins are in fact part of a
loop filter.
T and Q This is a wave-shaping circuit found in a few NEC chips (uPD2810, uPD2814, uPD2816, and
uPD2824). It adds design flexibility but is often not even connected. This circuit consistsofan input
amplifier and a ''flip-flop'', and its purposeis to change asine-wave input (T) to a square-wave output
(Q) which is more compatible with digital electronic circuits.
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