User manual

Page 11

Document No. 80-15151 Issue 6 HEBER LTD

Note that this scrambling of address lines is applicable ONLY to sockets U1 and U2 on the Pluto 5

Controller Board. Any EPROM sockets on Memory Expansion Cards are connected 1:1 to the

address bus and do NOT require any special processing.

5.7 EPROM Address Line Scrambling in 16 Bit Mode

5.7.1 2*27C040 EPROMs

In 16 bit mode, running with 2 * 27C040 EPROMs, the scrambling of the address lines cause the

following effect on the memory mapping in the EPROMs. Note that this table applies to the re-mapping

that occurs to the EPROM contents, rather than the actual address lines.

Table 6. Re-Mapping of Address Lines in 2*27C040 Mode

68340 Address Bus EPROM Address

A0 Not Used in 16 Bit Mode

A1-A18 A2-A19

A19 A1

Thus, for example, addresses will be translated as follows so the contents of the EPROM must be re-

arranged to compensate:

Table 7. Re-Mapping of EPROM Contents in 2*27C040 Mode

68340 Access Address Will Read From This Location in

EPROM

0000 0000 0000 0000

0000 0002 0000 0004

0000 0004 0000 0008

0000 0006 0000 000C

0000 0008 0000 0010

0007 FFFC 000F FFF8

0007 FFFE 000F FFFC

0008 0000 0000 0002

0008 0002 0000 0006

000F FFFC 000F FFFA

000F FFFE 000F FFFE

5.7.2 2*27C801 EPROMs

In 16 bit mode, running with 2 * 27C801 EPROMs, the scrambling of the address lines cause the