Specifications

WDTR If 1, expiration of the .i.watchdog timer; generates a .i.reset; of the
EPC-2. If 0, only the WDT event is signalled.
FWDT Fast .i.watchdog timer;. If clear, the period of the watchdog timer is
about 6.7 seconds. If set, the period is about 210 ms.
A read of the MSC register also has a side effect of resetting the watchdog
timer. Therefore, if you are using the watchdog timer, the intention is that
you are required to read this register within the defined period of the timer to
prevent its generating an interrupt.
.i.Signal Register FIFO; (.i.SRF;)
815E
815F
If the signal register FIFO is not empty, a read of these registers returns the
oldest value in the FIFO. The value is removed from the FIFO upon reading of
the "lower" byte (port 815E). If the FIFO is empty, the value returned is not
specified.
Register State after Reset
A .i.hardware reset; of the EPC-2 (not a keyboard CTRL+ALT+DEL reset) clears all
of the register bits to 0 (except those defined as a constant 1). The EPC-2's
BIOS, however, initializes some of the registers based on information from the
setup screen and elsewhere. The BIOS clears the .i.BIE; and .i.BEE; interrupt
and event enable registers.
POS Register
The EPC-2 contains a .i.nonvolatile option register;, or .i.POS register;,
containing information maintained by the BIOS. The information includes the
.i.slot 0; enable, bus .i.arbitration priority;, .i.bus release mode;,
.i.monitor type;, .i.arbitration mode;, DRAM size, .i.external clock; enable,
and parallel port mode. Since the POS register is closely allied with correct
operation of the BIOS, it is not user programmable; thus programming information
is not provided in this manual.
VMEbus Accesses
Two C-language examples are given here for performing .i.VMEbus accesses;
(accesses to the VXI .i.data transfer bus;) through the .i.E page;. The first
performs a 16-bit read from the VMEbus A16 space. It requires setting the
.i.address modifier;, relocating the A16 address into the E page (address range
E0000-EFFFF), and then accessing the value pointed to by a C pointer variable.
#define WORD unsigned short
#define LWORD unsigned long
WORD addr; /* 16-bit A16 address */
WORD data;
WORD far * wptr;
outp(0x8130,0); /* Set up E page as one contiguous region */
outp(0x8132,1);
outp(0x8134,2);
outp(0x8136,3);
outp(0x8151,0x0A); /* Set address modifier to A16 supervisory access */
wptr = (WORD far *) (0xE0000000L + addr);
data = *wptr; /* Read through window */
The next example does a byte write into the VMEbus .i.A32; space. Here the
upper 16 bits of the VME address need to be stored in the appropriate registers.
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