| Pin | Name | Description |
|---|
| 1 | PDA | Analog output from the sample and hold phase comparator for use as a ‘fine’ error signal.
Output at
(VDD 2VSS)/2 when the system is in lock.
Voltage increases as fv phase lead increases; voltage
decreases as fr phase lead increases.
Output is linear over only a narrow phase window, determined
by gain (programmed by RB). |
| 2 | PDB | Three-state output from the phase/frequency detector for use as a ‘coarse’ error signal.
fv > fr or fv leading: positive pulses with respect to the bias point VBIAS
fv r or fr leading: negative pulses with respect to the bias point VBIAS
fv = fr and phase error within PDA window: high impedance. |
| 3 | LD | An open-drain lock detect output at low level when phase error is within PDA window (in lock); high
impedance at all other times. |
| 4 | FIN | The input to the main counters, normally driven from a prescaler, which may be AC-coupled or, when
a full logic swing is available, may be DC-coupled. |
| 5 | VSS | Negative supply (ground). |
| 6 | VDD | Positive supply. |
7
8 | OSCIN
OSCOUT | These pins form an on-chip reference oscillator when a series resonant crystal is connected across
them. Capacitors of appropriate value are also required between each end of the crystal and ground
to provide the necessary additional phase shift. An external reference signal may, alternatively, be
applied to OSCIN. This may be a low-level signal, AC-coupled, or if a full logic swing is available it may
be DC-coupled. The program range of the reference counter is 3 to 2047, with the division ratio being
twice the programmed number. |
| 9 | NC | Not connected. |
| 10 | DATA | Information on this input is transferred to the internal data latches during the appropriate data read time
slot. DATA is high for a ‘1’ and low for a ‘0’. There are three data words which control the NJ88C24;
MSB is first in the order: ‘A’ (7 bits), ‘M’ (10 bits), ‘R’ (11 bits). |
| 11 | CLOCK | Data is clocked on the negative transition of the CLOCK waveform. If less than 28 negative clock
transitions have been received when the ENABLE line goes low (i.e., only ‘M’ and ‘A’ will have been
clocked in), then the ‘R’ counter latch will remain unchanged and only ‘M’ and ‘A’ will be transferred from
the input shift register to the counter latches. This will protect the ‘R’ counter from being corrupted by
any glitches on the clock line after only ‘M’ and ‘A’ have been loaded If 28 negative transitions have
been counted, then the ‘R’ counter will be loaded with the new data. |
| 12 | ENABLE | When ENABLE is low, the DATA and CLOCK inputs are disabled internally. As soon as ENABLE is
high, the DATA and CLOCK inputs are enabled and data may be clocked into the device. The data is
transferred from the input shift register to the counter latches on the negative transition of the ENABLE
input and both inputs to the phase detector are synchronised to each other. |
| 13 | CAP | This pin allows an external capacitor to be connected in parallel with the internal ramp capacitor and
allows further programming of the device. (This capacitor is connected from CAP to VSS |
| 14 | MC | Modulus control output for controlling an external dual-modulus prescaler. MC will be low at the beginning
of a count cycle and will remain low until the ‘A’ counter completes its cycle. MC then goes high and
remains high until the ‘M’ counter completes its cycle, at which point both ‘A’ and ‘M’ counters are reset.
This gives a total division ratio of MP+A, where P and P+1 represent the dual-modulus prescaler
values. The program range of the ‘A’ counter is 0-127 and therefore can control prescalers with a
division ratio up to and including divided by 128/129. The programming range of the ‘M’ counter is 8-1023
and, for correct operation, M>A or M=A. Where every possible channel is required, the minimum total division
ratio should be: N > P2 - P or N = P2 - P, where N=MP+A |
| 15 | RB | An external sample and hold phase comparator gain programming resistor should be connected
between this pin and VSS. |
| 26 | CH | An external hold capacitor should be connected between this pin and VSS |