D17133CS datasheet(90/289 Pages) NEC

90 / 289 page

CHAPTER 9

9.3 CONTROL REGISTER

The control register consists of 64 nibbles (64

× 4 bits) allocated in register file address locations 00H to 3FH.

Of these nibbles, only 17 nibbles are actually used in the

µPD17120 and 17121, and 20 nibbles are used in the

µPD17132, 17133, 17P132, and 17P133.

There are two types of registers, both of which occupy one nibble of memory. One type is read/write (R/W), and

the other is read-only (R).

Note that within the read/write (R/W) flags, there exists a flag that will always be read as 0.

The following read/write (R/W) flags are those flags which will always be read as 0:

• TMRES

(RF: 11H, bit 2)

Within the four bits of data in a nibble, there are bits which are fixed at 0 and will therefore always be read as

0. These bits remain fixed at 0 even when an attempt is made to write to them.

Attempting to read data in the unused register address area will yield unpredictable values. In addition, attempting

to write to this area has no effect.

Concerning the configuration of control register, refer to Figures 19-1 and 19-2.

9.4 CAUTIONS ON USING THE REGISTER FILE

9.4.1 Concerning Operation of the Control Register (Read-Only and Unused Registers)

It is necessary to take note of the following notes concerning device operation and use of the 17K Series assembler

(AS17K) and in-circuit emulator (IE-17K or IE-17K-ET) with regard to the read-only (R) and unused registers in the

control register (register file address locations 00H to 3FH).

(1) Device operation

Writing to a read-only register has no effect.

Attempting to read data from an address in the unused data area will yield an unpredictable value. Attempting

to write to an address in the unused data area has no effect.

(2) During use of the assembler (AS17K)

An error will be generated if an attempt is made to write to a read-only register.

An error will also be generated if an attempt is made to read from or write to an address in the unused data

area.

D17133CS датащи(PDF) 90 Page - NEC