MITSUBISHI MICROCOMPUTERS
M37754M8C-XXXGP, M37754M8C-XXXHP
M37754S4CGP, M37754S4CHP
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
RESET CIRCUIT
INPUT/OUTPUT PINS
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Reset is released when the RESET pin is returned to “H” level after
holding it at “L” level while the supply voltage is at 5V ±10%. As the
result, program execution starts at the address formed by setting the
address A23–A16 to 0016, A15–A8 to the contents of address FFFF16,
and A7–A0 to the contents of address FFFE16.
Ports P0 to P11 all have the direction register and each bit can be
programmed for input or output. A pin becomes an output pin when
the corresponding bit of direction register is “1”, and an input pin
when it is “0”.
When a pin is programmed for output, the data is written to its port
latch and it is output to the output pin. When a pin is programmed for
output, the contents of the port latch is read instead of the value of
the pin. Accordingly, a previously output value can be read correctly
even when the output “H” voltage is lowered or the output “L” voltage
is raised owing to an external load and others.
Figure 76 shows the status of the internal registers during reset.
Figure 77 shows an example of a reset circuit. When a stabilized
clock is input from the external to the oscillation circuit, the reset in-
put voltage must be held 0.9V or lower when the supply voltage
reaches 4.5V. When connecting a resonator to the oscillation circuit,
return the reset input voltage from “L” to “H” after the main-clock os-
cillation is fully stabilized
A pin programmed as an input pin is floating, and the value input to
the pin can be read. When a pin is programmed as an input pin, the
data is written only in the port latch and the pin remains floating.
Additionally, ports P95, P54 to P57 include pull-up transistors. The
pull-up function of ports is selected with bits 7 and 6 of the particular
function select register 1. Refer to the section on Interrupts for the
pull-up function.
Power on
Figures 78 and 79 show block diagrams of ports P0 to P11 in the
_
single-chip mode and E output.
4.5V
VCC
RESET
VCC
0 V
Ports P0 to P4, P10 and P11 are also used as pins of address, data
and control signals. Refer to the section on Processor mode for more
details.
RESET
0 V
0.9V
Fig. 77 Reset circuit example (perform careful evaluation at system
design before using)
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RENESAS [ RENESAS TECHNOLOGY CORP ]
