Appendix D List Of Cautions - NEC 78K0S/KB1+ User Manual

This appendix lists cautions described in this document.
"Classification (hard/soft)" in table is as follows.
Hard: Cautions for microcontroller internal/external hardware
Soft: Cautions for software such as register settings or programs
Function Details of
Function
Pin AV pin
SS
configu-
ration
Pin P121/X1 and
functions P122/X2 pins
Memory Vector table
space address
SP: Stack pointer
Port P121/X1 and
functions P122/X2 pins
P34 pin
P30, P31, and
P43 pins
PMC: Port mode
control register 2
−

APPENDIX D LIST OF CAUTIONS

Connect the AV pin to V
SS SS
The P121/X1 and P122/X2 pins are pulled down during reset.
No interrupt sources correspond to the vector table address 0014H.
Since generation of reset signal makes the SP contents undefined, be sure to
initialize the SP before using the stack memory.
Stack pointers can be set only to the high-speed RAM area, and only the lower
10 bits can be actually set. Thus, if the stack pointer is specified to 0FF00H, it
is converted to 0FB00H in the high-speed RAM area, since 0FF00H is in the
SFR area and not in the high-speed RAM area.
When the value is actually pushed onto the stack, 1 is subtracted from
0FB00H to become 0FAFFH, but since that value is not in the high-speed
RAM area, it is converted to 0FEFFH, which is the same value as when
0FF00H is set to the stack pointer.
The P121/X1 and P122/X2 pins are pulled down during reset.
Because the P34 pin functions alternately as the RESET pin, if it is used as an
input port pin, the function to input an external reset signal to the RESET pin
cannot be used. The function of the port is selected by the option byte. For
details, refer to CHAPTER 18 OPTION BYTE.
Also, since the option byte is referenced after the reset release, if low level is
input to the RESET pin before the referencing, then the reset state is not
released. When it is used as an input port pin, connect the pull-up resistor.
Because P30, P31, and P43 are also used as external interrupt pins, the
corresponding interrupt request flag is set if each of these pins is set to the
output mode and its output level is changed. To use the port pin in the output
mode, therefore, set the corresponding interrupt mask flag to 1 in advance.
When PMC20 to PMC23 are set to 1, the P20/ANI0 to P23/ANI3 pins cannot
be used as port pins. Moreover, be sure to set the pull-up resistor option
registers (PU20 to PU23) to 0 for the pins set to A/D converter mode.
Although a 1-bit memory manipulation instruction manipulates 1 bit, it
accesses a port in 8-bit units. Therefore, the contents of the output latch of a
pin in the input mode, even if it is not subject to manipulation by the
instruction, are undefined in a port with a mixture of inputs and outputs.
User's Manual U17446EJ3V1UD
Cautions
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