Specifications

Chapter 4: Theory of Operation
35
and quickly place the new battery into the empty socket. Replace the SIMM module and
reinsert the EPC-8A into the system.
Peripheral Ports
The I/O address and IRQ of the peripheral ports are determined by the CMOS parameters
established by default and modified via BIOS Setup screens.
RS-232 Port
The RS-232 port is a standard PC COM port based on the 16550 architecture. It is
normally configured as COM1 (I/O address = 3F8–3FF, IRQ4). “COM1” is an alias for an
address and is determined by the first COM port found. If not needed, COM1 can be
disabled in the BIOS Setup screen to free up the I/O address and interrupt for usage by
other expansion products.
RS-422/485 Port
The modified RS-422/RS-485 port is normally configured as COM2 (I/O address = 2F8–
2FF, IRQ3). This port is also a standard PC COM port based on the 16550 architecture. If
not needed, COM2 can be disabled in the setup screen to free up the I/O address and
interrupt for usage by other expansion products. The RXD and TXD signals are RS422
compatible with differential receiver and driver, respectively. Handshake signals RTS,
DTR, CTS and DSR are single-ended RS422 compatible. Outputs TXD+ and TXD- are
tristated if RTS is unasserted for RS485 multidrop compatibility. The port has 10K ohm
termination.
Parallel Port
The printer port is a standard PC printer port. The parallel port supports bi-directional
communication compatible with the PS/2 definition. It is configured as LPT1 (I/O address
378–37F, IRQ7). If not needed, LPT1 can be disabled in the setup screen to free up the I/O
address and interrupt for usage by other expansion products.
Keyboard
The keyboard controller is integrated into the RadiSys chipset. It can interface to most
standard PC keyboards with a PS/2-style connector. An adapter cable is shipped with the
EPC-8A to allow use of standard PC/AT keyboards with larger 5-pin connectors.
Front Panel LEDs
The EPC-8A has three LEDs in the top left corner of the front panel. These LEDs are
described below:
RUN This LED is lit whenever a write access to DRAM is made. This provides a
normally lit LED indicating that the CPU is operating. This LED is not lit if the
CPU is halted or is executing entirely out of the on-chip cache.
FAIL This LED is lit whenever the VME SYSFAIL line is asserted if the EPC-8A is
jumpered to be the Slot-1 controller. This occurs independent of which VME
board is driving the SYSFAIL line. It comes on whenever the system receives
a hardware reset and remains on until the initial power-on self-tests complete.