UPD17P136ACT datasheet(84/292 Pages) NEC

84 / 292 page

CHAPTER 7 SYSTEM REGISTER (SYSREG)

7.8.2 Handling of System Register Addresses Fixed at 0

In dealing with system register area fixed at 0 (see Figure 7-2), there are a few points for which caution should

be taken with regard to device, emulator and assembler operation.

Items (1), (2) and (3) explain these points.

(1) Concerning device operation

Trying to write data to an address fixed at 0 will not change the value (0) at that address. Any attempt to read

an address fixed at 0 will result in the value 0 being read.

(2) When using a 17K series in-circuit emulator (IE-17K or IE-17K-ET)

An error will be generated if a write instruction attempts to write 1 to an address fixed at 0.

Below is an example of the type of instructions that will cause the in-circuit emulator to generate an error.

Example 1.

MOV

BANK, #0100B

; Attempts to write 1 to bit 3 (an address fixed at 0).

MOV

IXL, #1111B

;

MOV

IXM, #1111B

;

MOV

IXH, #0001B

; Attempts to write 1 to bit 0 (an address fixed at 0).

ADD

IXL, #1

;

ADDC

IXM, #0

;

ADDC

IXH, #0

; Attempts to write 1 to bit 0 (an address fixed at 0) as a result of

operation.

However, when all valid bits are set to 1 as shown in Example 2, executing the instructions INC AR or INC

IX will not cause an error to be generated by the in-circuit emulator. This is because when all valid bits of the

address register and index register are set to 1, executing the INC instruction causes all bits to be set to 0.

The only time the in-circuit emulator will not generate an error when an attempt is made to write the value 1

to an address fixed at 0 is when the address being written to is in the address register.

(3) When using a 17K series assembler (AS17K)

No error is output when an attempt is made to write 1 to an address fixed at 0. The instruction shown in

Example 1

MOV

BANK, #0100B

will not cause an assembler error. However, when the instruction is executed in the in-circuit emulator, an

error is generated.

The following is the reason why an error is not generated in the assembler: the assembler does not know what

data memory address is the object of the data memory manipulation instruction being executed.

The assembler generates an error only when the value n in the embedded macro BANKn is a value greater

than 2:

This is because the assembler judges that embedded macros other than BANK0 and 1 cannot be used in the

µPD17134A subseries.

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