HD6433308 Datasheet, PDF (39/349 Pages) Hitachi Semiconductor – Hitachi Single-Chip MicroComputer

2.4.2 System Control Register (SYSCR) – H’FFC4
By setting or clearing the lower two bits of the system control register, software can enable or
disable the on-chip RAM and dual-port RAM.
The other bits in the system control register concern the software standby mode and the valid edge
of the NMI signal. These bits will be described in section 4, “Exception Handling” and section 14,
“Power-Down State.”
Bit
Initial value
Read/Write
7
SSBY
0
R/W
6
STS2
0
R/W
5
STS1
0
R/W
4
STS0
0
R/W
3
2
1
0
— NMIEG DPME RAME
1
0
0
1
—
R/W R/W R/W
Bit 1—Dual-Port RAM Enable (DPME): In the single-chip mode, this bit enables or disables the
dual-port RAM. When enabled, the dual-port RAM can be accessed by both an external (master)
CPU and the on-chip (slave) CPU. When disabled, the dual-port RAM can be accessed only by the
on-chip CPU.
This bit affects the usage of ports 3, 8, and 9.
Bit 1
DPME
0
1
Description
The dual-port RAM is disabled. (Initial state)
Single-chip mode: The dual-port RAM is enabled (slave mode).
Expanded modes: The dual-port RAM is disabled (but can be accessed by the on-chip
CPU).
Bit 0—RAM Enable (RAME): This bit enables or disables the 512-byte on-chip RAM. When
enabled, the on-chip RAM occupies addresses H’FD80 to H’FF7F of the address space. When the
on-chip RAM is disabled, accesses to these addresses are directed off-chip.
The RAME bit is initialized to "1" by a reset, enabling the on-chip RAM. The setting of the
RAME bit is not altered in the sleep mode or software standby mode. It should be cleared to "0"
before entering the hardware standby mode. See section 14, "Power-Down State."
Bit 0
RAME
0
1
Description
The on-chip RAM is disabled.
The on-chip RAM is enabled.
(Initial state)
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