M16C/62P Group (M16C/62P, M16C/62PT)
8. Bus
Rev.2.41
Jan 10, 2006
Page 65 of 390
REJ09B0185-0241
8.2.7
HOLD Signal
This signal is used to transfer control of the bus from the CPU or DMAC to an external circuit. When the input
on HOLD pin is pulled low, the microcomputer is placed in a hold state after the bus access then in process
finishes. The microcomputer remains in the hold state while the HOLD pin is held low, during which time the
HLDA pin outputs a low-level signal.
Table 8.5 shows the Microcomputer Status in Hold State.
Bus-using priorities are given to HOLD, DMAC, and CPU in order of decreasing precedence. However, if the
CPU is accessing an odd address in word units, the DMAC cannot gain control of the bus during two separate
accesses.
Figure 8.5
Bus-Using Priorities
NOTES:
1. P11 to P14 are included in the 128-pin version.
2. When I/O port function is selected.
3. The watchdog timer dose not stop when the PM22 bit in the PM2 register is set to “1” (the count
source for the watchdog timer is the on-chip oscillator clock).
8.2.8
8.2.8 BCLK Output
If the PM07 bit in the PM0 register is set to “0” (output enable), a clock with the same frequency as that of the
CPU clock is output as BCLK from the BCLK pin. Refer to
10.2 CPU Clock and Peripheral Function Clock
.
Table 8.5
Microcomputer Status in Hold State
Item
Status
BCLK
Output
A0 to A19, D0 to D15, CS0 to CS3, RD, WRL,WRH,
WR, BHE
High-impedance
I/O ports
P0, P1, P3, P4
(2)
High-impedance
P6 to P14
(1)
Maintains status when HOLD signal is received
HLDA
Output “L”
Internal Peripheral Circuits
ON (but watchdog timer stops)
(3)
ALE Signal
Undefined
HOLD > DMAC > CPU
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