UPD17217CT datasheet(20/84 Pages) NEC

20 / 84 page

µPD17215, 17216, 17217, 17218

(3)

Note on using data buffer

When transferring data to/from the peripheral hardware via the data buffer, the unused peripheral addresses,

write-only peripheral registers (only when executing PUT), and read-only peripheral registers (only when

executing GET) must be handled as follows:

• When device operates

Nothing changes even if data is written to the read-only register.

If the unused address is read, an undefined value is read. Nothing changes even if data is written to that

address.

• Using assembler

An error occurs if an instruction is executed to read a write-only register.

Again, an error occurs if an instruction is executed to write data to a read-only register.

An error also occurs if an instruction is executed to read or write an unused address.

• If an in-circuit emulator (IE-17K or IE-17K-ET) is used (when instruction is executed for patch processing)

An undefined value is read if an attempt is made to read the data of a write-only register, but an error does

not occur.

Nothing changes even if data is written to a read-only register, and an error does not occur.

An undefined value is read if an unused address is read; nothing changes even if data is written to this

address. An error does not occur.

UPD17217CT Datasheet(PDF) 20 Page - NEC