Table of Contents
Advertisement
WJ-8718A/MFP
TABLE 3-14
does not change the status of the device. After' the microprocessor replaces the addr-ess on the
bus with data, the WR line goes high and U11 is disabled. The U11 output that went low when
the WR line was low now changes state; this positive-going clock transition latches the data
into the addressed device.
Table 3-14. U11 Truth Table
Inputs
Outputs
Enable
Select
G1
G2A
G2B
AO
Al
A2
YO
Y1
Y2
Y3
Y4
Y5
Y6
H
L
L
L
L
L
L
H
H
H
H
H
H
H
L
L
H
L
L
H
L
H
H
H
H
H
H
L
L
L
H
L
H
H
L
H
H
H
H
H
L
L
H
H
L
H
H
H
L
H
H
H
H
L
L
L
L
H
H
H
H
H
L
H
H
H
L
L
H
L
H
H
H
H
H
H
L
H
H
L
L
L
H
H
H
H
H
H
H
H
L
3.2.5.4
RF Gain Conversion
D/A
(U23)
Digital-to-analog (D/A) converter U23 at address 1013 is used during scan
operation during BITE tests, or if the receiver is under remote control. The 8-bit binary-coded
RF gain word is latched into its inputs when the WR1 input is pulsed low during a WR cycle
from the Y3 output of address decoder Ull.
The converter provides an output current directly related to the coded RF gain
word. The current is converted to a positive voltage by amplifier U24C through feedback input
RFB.
The output voltage is derived from a R-2R ladder network which can be deduced
mathematically by the equation:
yREF
binary input x
~
=
output voltage.
Where yREF is derived from YR1 zener diode through the -15
V
supply.
The symbol yREF
equals -5.1 y, so a binary input bit multiplied by .019
V
is an approximation of the output
voltage.
3.2.5.5
Audio/Gain Switch (U22)
Analog switch U22 is a triple two-channel multiplexer, housing three separate
digital control inputs:
A, B, and C. Each input controls a pair of channels connected in a
single-pole double-throw configuration.
Input A controls channel X which selects the RF gain voltage. Input A is tied to
the remote/local latch U21B. When the receiver is in the local mode, the A input is held low
and the RF gain potentiometer voltage is fed through channel XO to X. When the receiver is in
the remote mode, the A input is held high and the digital-to-analog RF gain voltage is fed
through channel Xl to X.
3-37
Advertisement
Chapters
Table of Contents
