112
4.2.9
DRAM Access Control Register (DRACCR)
Bit
7
6
5
4
3
2
1
0
DRMI
—
TPC1
TPC0
—
—
RCD1
RCD0
Initial value
0
0
0
0
0
0
0
0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
DRACCR is an 8-bit readable/writable register used to set the DRAM interface bus specifications.
DRACCR is initialized to H'00 by a reset and in hardware standby mode. It is not initialized in
software standby mode.
Bit 7—Idle Cycle Insertion (DRMI): Selects whether or not an idle cycle is inserted when a
normal access cycle follows a DRAM read cycle.
Bit 7
DRMI
Description
0
Idle cycle not inserted after DRAM space access
(Initial value)
1
Idle cycle inserted after DRAM space access
Idle cycle insertion conditions, setting of number of states, etc., comply with settings
of bits ICIS1, ICIS0, and IDLC in BCR register
Bit 6—Reserved: This is a readable/writable bit, but the write value should always be 0.
Bits 5 and 4—Precharge State Control (TPC1, TPC0): These bits select the number of states in
the RAS precharge cycle in normal access and refreshing. From 1 to 4 states can be set for the
precharge cycle.
Bit 5
TPC1
Bit 4
TPC0
Description
0
0
RAS
precharge cycle comprises 1 state
(Initial value)
1
RAS
precharge cycle comprises 2 states
1
0
RAS
precharge cycle comprises 3 states
1
RAS
precharge cycle comprises 4 states
Bits 3 and 2—Reserved: These are readable/writable bits, but the write value should always be 0.
Bits 1 and 0—RAS-CAS Wait Control (RCD1, RCD0): These bits select whether or not a wait
cycle is to be inserted between the
RAS
assert cycle and
CAS
assert cycle. A 1- to 4-state wait
cycle can be inserted.
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