NEC PD78P214 Manuale Utente

93

Chapter 5   Port Functions

Port 7 is an input-only port, and the level of its pins can be read and tested.

Internal bus

RD

IN

P7n
n = 0 to 5

Port 0 has no built-in pull-up resistor.

(1) When P70 through P75 are used as analog input pins AN0 and AN5 respectively or when A/D conversion is

not performed, do not apply a voltage out of the range AV

SS

 through AV

REF

 to the pins that are selected for

ANI0 through ANI2 of the A/D converter mode register (ADM).

See Chapter 8 for details.

(2) Port 7 is a 6-bit input port.  The upper 2 bits of “8-bit” data from port 7 are undefined.

(1) When the RESET signal is input, all the port pins are set to high-impedance (disconnected from their built-in

pull-up resistors).

If it is necessary to prevent a port pin from being set to high-impedance state when the RESET signal is being
supplied, take an appropriate action using an external circuit.

(2) Some operations of the pull-up-resistor-option register (PUO), which is used to specify connection of built-

in pull-up resistors, cannot be emulated by an in-circuit emulator, because of the following restrictions:

• The contents of the PUO register cannot be read correctly.

• Bit manipulation instructions or logical/arithmetic instructions do not work for the PUO register; an SFR

illegal access break may occur, aborting emulation.

• No built-in pull-up resistor is provided.

Therefore, observe the following two points.

• To set the PUO register, use only an 8-bit data transfer instruction (MOV).

• When debugging the target board, use pull-up resistors provided on it.

(3) Supplying the RESET signal does not initialize the contents of the output latch.  When using a port in the output

mode, initialize the output latch before turning on the output buffer.  Otherwise, data output from the output
ports is unpredictable.

Similarly, to use a port as a control pin, always initialize the internal hardware before specifying the control
pin.