A3.3 Ems 110 Port Address Selections - Everex EV-159 Owner's Manual And Reference Manual

A3.3 EMS I/O Port Address Selections
EMS uses 110 ports to set up mapping information. These
1/0 ports are selectable and a number of 110 ports have
been reserved for EMS memory. These ports are:
Mapping Registers
02X8:
42X8:
82X8:
C2X8:
page 1
page 2
page 3
page 4
Page Frame Registers
02X9
42X9
82X9
where the variable X is selectable in a range from
0
to E.
The page frame registers determine the starting address of
the EMS window in the CPU addressing space, while the
mapping registers determine which 16K page of physical
memory of the EMS board is to be mapped into the
window.
Each RAM 3000 Deluxe has four 16K pages that map into
the 64K window, yet at anyone time there should not be
more than one active page in the same page location within
the window. By controlling the MSB of the mapping regis-
ter, one can enable or disable the corresponding page. As a
result, more than one EMS card can be used. According to
specification, EMS can support up to 8MB of memory.
75