Sharp MZ-700 manual 1Z-700

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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	INHl	INH2	INH3
	~	l
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
$E6		Returns to the		-
	-	state before	-		H
		prohibitied.

INHl - INH3 are custom LSI internal signals which cause the memory map to change.

INH1	H	L	H		H
INH2	H	H	L		H
INH3	H	H	H		L
		1--:-.:-:-:---1		I ::: I
	I--D-_R:_:_M---I		I---D-_:_OA_MM----j
	V·RAM	V·RAM	D-RAM
					L
INH1	L	H	L
INH2	L	L	H		L
INH3	H	L	L		L
	D·RAM	ROM	D-RAM		D-RAM
	D-RAM	D-RAM	D-RAM		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.

•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, WATN 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.

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