Sharp MZ-700 Service Manual page 8

\ ,'1Z -700
2) Memory controller
In the MZ· 700, it needs to segregate the memory in order
to acheive the above mentioned memory mapping. The
memory controller is therefore used to perform address
management of peripherals assigned to the memory such
as DRAM, monitor ROM, video RAM, and keyboard. The
bank select method is used to switch memory. Memory
selection is acheived using the OUT command.
I/O
$0000 $DOOOO
~ l INHl INH2 INH3
port
$OFFF $FFFF
$EO D·RAM
-
L
-
-
$El
-
D-RAM
-
L
-
$E2
MONITOR
H
ROM
- - -
$E3
-
V·RAM,8255
-
H -
8253
$E4
MONITOR V·RAM,8255
H H H
ROM
8253
$E5
-
Prohibited
- -
L
Returns to the
$E6 - state before
-
-
H
prohibitied.
INHl - INH3 are custom LSI internal signals which cause
the memory map to change.
INH1
INH2
INH3
INH1
INH2
INH3
H L H H
H H L H
H H H L
I--D-_R:_:_M---I
1--:-.:-:-:---1
I---D-_:_OA_MM----j
I ::: I
V·RAM V·RAM D-RAM
L
L
H
D·RAM
D-RAM
D·RAM
H
L
L
ROM
D-RAM
L
H
L
D-RAM
D-RAM
L
L
L
D-RAM
D·RAM
NOTE: The command with which the memory selection is
to be done should not be written in the memory
block to be selected.
7
• Custom LSI internal memory controller block diagram
and description
When the above mentioned OUT command is executed,
address Ao ,.., A2 is stored in "FF" to create INHl ,..,
INH3, then ROM, VRAM, and DRAM may be accessed
against CPU addressing on the basis of those INH signals.
•
RA~
becomes active when the DRAM is accessed.
• CSO becomes active when the monitor ROM is accessed.
• CSE becomes active when the memory mapped I/O
(8255,8253)
is
accessed.
• CSDN (internal signal) becomes active when the VRAM
is accessed. If in the blnk period, CSDD becomes active.
So
that, the address from the CPU is sent of Po ,.., PlO.
• If the display period
is
on when accessing the ROM or
VRAM, W ATN becomes active.
• line address and row address switching signal (LS157
input) when accessing the RAM is derived from PHI,
WRN, MRQN, and RDN. As WR rises before the falling
edge of CAS during the write cycle, it becomes an early
cycle.