VC3500/VC3700 Troubleshooting Manual
Valco Cincinnati
Page 10
Schematic Description
Main Processor
A 68000 (U1) performs the following functions:
•
Control of LCD/Touchscreen module.
•
Storage of glue programs.
•
Communications with Channel Logic processors.
Reset/Watchdog Circuit
A DS1232 (U6) provides both reset and watchdog functions. "/DTACK" must occur every
150mS (typical) or a reset will occur. The reset signal is buffered by open-collector drivers
(U8) because the "/HALT" and "/RESET" signals can be both read and driven by the 68000.
Clock Circuits
An 8 MHz oscillator (U7) provides timing for the 68000. The 87C51's (U18, 19, 20) each
have a 12 MHz crystal.
Address Decode Circuit and /DTACK
74HCT138's (U10,12) provide all address decoding. These decoding signals are OR'ed
together to derive the "/DTACK" signal required by the 68000. A "/DTACK" signal
returned to the 68000 indicates that a peripheral device has read or written data to the bus,
and therefore the 68000 can continue with the next program step.
Operating System Memory
27C512 PROM's (U4,5) are used to store the operating system. Two-channel software
resides in the lower half, and four-channel software resides in the upper half. A jumper near
the center of the board should be installed (or switch set to 'ON') so the lower half of memory
is enabled (two-channel). This jumper should be cut (or switch set to 'OFF') to enable the
upper half of memory (four-channel).
Battery-Backed Program Memory
BQ4011 RAM's (U2,3) store program parameters
Touchscreen Interface
74HCT245 bi-directional buffers (U15,16) pass the data and control signals to the
LCD/Touchscreen. U15 is fixed to only send address and control signals. U16 is controlled
by "R/W" to determine the direction of data flow.
Encoder Count Circuit (Speed Calculation)
A timer within U17 (68230) outputs an active-low signal for 100mS from its port at PB6 to
U8.3. This open-collector output (U8.4), when high, allows encoder pulses to pass to the
clock input of a 74HCT393 counter (U9.1). Periodically, the 68000 will read this counter's
8-bit output through port PA of U17 (68230) and calculate the line speed. The 68000 uses
this information to size the length of the bar graph in the Minimum Speed screen to indicate
line speed.
Auxiliary Port Signals (U14-68230)
Port PC of U14 is used as the data link between the 68000 and the Channel Logic processors
(U19,20). Port PB of U14 is used to control the flow of data between these devices.
Summary of Contents for VC3500
Page 1: ...VC3500 User s Manual Software Version 3 X Manual Number MCO35 Manual Release Date July 1999 ...
Page 19: ...Installation VC3500 User s Manual Valco Cincinnati 16 Figure 8 Internal Connections Diagram ...
Page 88: ...VC3700 User s Manual Software Version 3 X Manual Number MCO34 Manual Release Date July 1999 ...
Page 181: ...VC3500 VC3700 Troubleshooting Manual Manual Number MC048 Release Date May 1999 ...
Page 185: ...VC3500 VC3700 Troubleshooting Manual Valco Cincinnati Page 1 System Level Documents ...