3-27
Data transfers betweenthe two processorsare initiated
by interrupts that signal the destination processorthat ser-
vice is requested.When the Front PanelMPhas changed-
value data to give to the System MP,it will place the data
Handshake Logic
The Handshake Logic circuit, formed by NOR-gates
U862A, B, C, and D and flip-flops U861A and B, controls
and synchronizesdata transfers between the System MP
and the Front Panel/-lP.
Jumper J155, connected to the PC?and PD?inputs, is
used to enable diagnostic test routines that verify func-
tionality of U700. The test routines may also be used to
troubleshoot the Front Panel Processor system. These
tests are explained in the Diagnostics portion of the
"Maintenance" section of this manual.
The WRTOFP (write to front-panel processor) input to
U700 at pin 3 is set LO (via the Handshake Logic) when
the SystemJ.lPwants to input data to the Front Panel/-lP.
The Front Panel/-lPthen reads one byte of data from the
System MPin a manner similar to that just describedfor
transfers from the Front PanelMPto the System /-lP.This
mode allows the System MPto change the current control
configuration list stored in the limited RAM space of the
Front Panel/-lP.This list defines how the operation of pots
and switches is to be interpreted(for example,momentary
contact or toggle switches).
The System /-lPthen reads the changed-databytes for
the identified control(s) (either three bytes or five bytes
depending on whether one or two control changes are
being sent) and reasserts HOSTDNRD.Changes of up to
two controls are rememberedby Front Panel/-lPU700 so
that if the System/-lPis busy, the control changes are not
lost while the Front Panel /-lP is waiting to make the
transfers. If more than two controls are changed before
the System /-lPhas time to read the changes, the oldest
changeis written over and lost.
The System/-lP handles the interrupt by reading the
byte from the Front PanelJ.lP; and then, via the
Handshake Logic, it resets flip-flop U861B to remove the
interrupt and set HOSTDNRD(host done reading)HI. This
signals the Front Panel /-lPthat the System /-lPhas read
the codeidentifying the changed control. The Front Panel
J.lPthen places the new control-setting value on its output
bus and reasserts the front-panel interrupt using the
WRTOHOSTlineto againclock flip-flop U861B.
Theory of Operation-2430 Service
When the Front Panel/-lP detects a change in either a
switch or a pot setting from its currently stored values, it
places a code identifying which control setting changed on
its PAO-PA7 outputs, and it then sets the WRTOHOST
(write to host) signal HI to clock Handshake Logic flip-flop
U861 B. The resulting HI on the
Q
output of the flip-flop is
the front-panel interrupt (FPINT)to the System /-lP,telling
it that the front-panelsettings havebeenchanged.
To read the front-panel switches, the Front Panel J.lP
first sets one of the front-panel switch-matrix rows LO,
using the MUXSELO-MUXSEL2 outputs. It then sets its
S/L (shift/load) output on pin 29 LO. The LO does a paral-
lel load of the switch-closure data into shift registers U904
(diagram 4) and U700 (diagram 6). The shift/load line is
then set HI (shift mode), and eight shift clocks (SHCLK)
are generated to move the switch-closure data serially
onto the SW OUT (front-panel switch data out) or the SW
OUT A (auxiliary front-panel switch data out) lines, where
it is read by the Front Panel /-lP. This cycle is then
repeated for the seven remaining rows of the matrix to
read all the switches.
To read front-panel pot settings, the internal A/D con-
verter of the Front Panel /-lP performs an 8-bit,
successive-approximation conversion of the analog levels
applied to the ANO and AN2 inputs by a selected poten-
tiometer. These analog input signals come from 8-input
analog multiplexers U902 on the Front Panel (diagram 4)
and U600 on the Auxiliary Front Panel (diagram 6). A
specific pot to be read is selected by the multiplexer under
control of the MUXSELO, MUXSEL 1, MUXSEL2, and
MUXINH (multiplexer inhibit) output lines from the Front
Panel J.lP. These select signals, in combination with the
selected A/D (ANO or AN2) input, define the pot being
read. The voltages monitored on the AN1 and AN3 analog
inputs are also digitized by the internal A/D converter to
detect Main board temperature (MBTEMP) changes (not
used at this time) and if lithium backup battery BT800
(diagram 1) is either low (needing replacement) or being
charged (not allowed).
main program routine sets up the data direction for the
various port lines, sets the ANO-AN3 (analog inputs 0-3) to
their analog input mode, and receives the eight front-panel
configuration bytes from the System/-lP that define the
manner in which the various front-panel switches and pots
operate. It then begins scanning the front-panel pots and
switches for their initial settings. After the initial values are
determined and stored, the Front Panel /-lP sends those
coded values back to the System /-lP in an 11-byte mes-
sage (10 data bytes plus an end-of-message byte) to
update the front-panel information held by the System /-lP.
It then begins scanning the front-panel controls for
changes from the currently stored front-panel values.
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