Specifications

EPC-8A Hardware Reference

for these bits. 2Dh = 00101101b

Bit 3 (Address Modifier bit 5) = 1

Bit 2 (Address Modifier bit 4) = 0

Bit 1 (Address Modifier bit 2) = 1

Bit 0 (Address Modifier bit 1) = 0

Thus, 8151h should be set to 1100 1010 or CAh.

1. Map the address.

Add the A16 address to the “E page” address

Addr

←

segment:offset + A16 address

2. Read the data.

Data

←

value pointed to by Addr

C code for Example 1

#define WORD unsigned short

#define LWORD unsigned long

WORD addr; /* 16-bit A16 address */

WORD data;

WORD far * wptr;

outp(0x8102,(inp(0x8102)|2));/* set VME E-page enable access bit */

outp(0x8151,0xCA); /* Set address modifier to A16 supervisory

access */

wptr = (WORD far *) (0xE0000000L + addr);

data = *wptr; /* Read through window */

Example #2

Example #2 performs a byte (8-bit) write into the VMEbus A32 space. Here the upper 16

bits of the VME address need to be stored in the appropriate registers.

1. Set the VME E-page enable bit in Register 8102h.

2. Set register 8150h with the value corresponding to the 8 high-order address bits.

3. Determine the correct address modifier for A32 supervisory access.

4. Calculate the value and set register 8151h as follows:

Bits 7 & 6 VME address bits 23–22

Bit 5 BORD = 0

Bit 4 IACK = 0

Bits 3–0 Bit 3 (Address Modifier bit 5)

Bit 2 (Address Modifier bit 4)

Bit 1 (Address Modifier bit 2)

Bit 0 (Address Modifier bit 1)

VMEbus Address bits 31–24 WA31–24

VME WA23–22 BORD IACK AM5 AM4 AM2 AM1