Keil MCB517AC, User Manual

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MCB517AC Evaluation Board User’s Guide 13
Decode Logic
All memory address decode logic as well as other signal conversion is performed
by two 20V8 PALs at IC13 and IC22. Refer to “ PAL Equations” on page 22 for
a complete listing of the PAL equations used.
Memory and I/O Devices
The MCB517AC maps three memory devices into the address space of the CPU.
RAM at IC5 and IC7, EPROM at IC23. The two 20V8 PALs at IC13 and IC22
provide also the chip select signal for the external CAN controller at IC3 and an
user chip select signal.
The MCB517AC board comes with an Monitor EPROM at IC23 which contains
up to 16 different Monitor versions. You can use 27C1001 or 27C2001 as an
USER EPROM at IC23. If you insert an EPROM with an user application
program, the DIP switch Monitor must be off. Then you can select different
memory bank options for the user application using the DIP switches S1 and S2.
For more information refer to “DIP Switches” on page 6.
Status LEDs
The MCB517AC has a single power LED labeled ON which indicates the power
to the board is on. Eight LEDs are optionally connected to the port 4 outputs
through a 74HC373 at IC2. The Port 4 LEDs are flashing during reset and
display the configuration status of the Monitor EPROM. For more information
refer to “Monitor Status Display” on page 10. You may disable the LED driver
by setting the LED DIP switch off. In this case you select also a Monitor
version which does not affect the Port 4 Pins during the reset phase.
Push Button
The MCB517AC provides one push button. It is labeled RESET (S1) and
connected to the reset input of the CPU. Pushing this button also resets the
external CAN controller 81C90.
Serial Port
The MCB517AC supports both on-chip serial ports of the 80C517A CPU. Both
of these use the MAX232 at IC9, to convert RS-232 voltage levels.