Raytheon Pathfinder 1200 Instruction Manual page 85

8) Sampling Clock OSC
The sampling clock oscillator consists of ICI4-11, IC14-6 and ICI4-8. The
output of IC22-9 is fed to IC14-13 and controls the oscillation. When IC14-13
is I state, the circuit of IC14-11 and IC14-6 oscillates and produces the pulse train.
The output frequency is adjusted to 17.5 MHz by CVI. The sampling clock pulse is
fed to the count down circuit via the buffer inverter IC14-8.
9) Count Down
The count down circuit produces the sampling clock pulses of I to 12 nm range.
"IC15 is two 4 stage FF. One of 4 stage FF is used as four 1/2 frequency dividers and
the other is used 1/3 divider with the feedback by IC76-6 and IC76-8.
10) Sampling Clock Select
The sampling clock select circuit produces the sampling clock pulse fitted on the
range which is set on the RANGE switches by selection from the output of sampling
clock OSC or the count down output.
The sampling clock frequency versus RANGE relation is as follows:
RANGE (nm)
0.25 0.5 2 4 8 12
Frequency (MHz)
17.5 17.5 8.75 4.375 2.1875 1.09375 0.72917
Period (usee)
0.057 0.057 0.114 0.229 0.457 0.914
1.371
IC 17 is the clock pulse select circuit for the pulse stretch circuit IC3. IC17-6
output is 17.5 MHz at 0.25 to 2 nm range and 4.375 MHz at 4 to 12 nm range.
11) R/W Clock Select
The read/write clock select circuit selects the pulse from the sampling clock pulses
and the display clock pulses by the sampling/displaying timing and the Range data.
At sampling time, this circuit selects the output of the sampling clock select circuit.
At the 0.25 nm range display time, this circuit selects 0.375 MHz pulse of H counter
and at the other range display time, this circuit selects 0.75 MHz pulse of H counter,
0.375 MHz and 0.75 MHz pulse are gated by IC24-3 and IC24-ll and are fed to
IC25 at the time of the video RAM writing only.
12) Memory Add Counter
The address counter IC 18/ 19 produces seven bits address data for the buffer
memory (lC7 AO-A6). IC20-12 produces the stop pulse after 112 pulses of the
input clock pulses.
13) W Pulse Generator
The W Pulse Generator IC72 produces the writing pulses to the video RAM
from the X address counter output XO and Xl. Four outputs of IC73 are added with
the video RAM clear pulse by IC74 and fed to four 16K bits dynamic RAM IC65 -68.
6-19