D17133CS datasheet(96/289 Pages) NEC

96 / 289 page

CHAPTER 10

DATA BUFFER (DBF)

10.2.1 Data Buffer and Peripheral Hardware

Table 10-1 shows data transfer with peripheral hardware using the data buffer.

Each unit of peripheral hardware has an individual address (called its peripheral address). By using this peripheral

address and the dedicated instructions GET and PUT, data can be transferred between each unit of peripheral

hardware and the data buffer.

GET DBF, p : Read the data in the peripheral hardware address specified by p into the data buffer (DBF).

PUT p, DBF:

Write the data in the data buffer to the peripheral hardware address specified by p.

There are three types of peripheral hardware units: read/write (PUT/GET), write-only (PUT) and read-only (GET).

The following describes what happens when a GET instruction is used with write-only hardware (PUT only) and

when a PUT instruction is used with read-only hardware (GET only).

• Reading (GET) from write-only (PUT only) peripheral hardware will yield an unpredictable value.

• Writing (PUT) to read-only (GET only) peripheral hardware has no effect (regarded as a NOP instruction).

Table 10-1. Peripheral Hardware

(1) Peripheral hardware with input/output in 8-bit units

Direction of Data

PUT

GET

01H

SIOSFR

Shift register

8 bits

02H

TMC

Timer count register

8 bits

03H

TMM

Timer modulo register

8 bits

(2) Peripheral hardware with input/output in 16-bit units

Direction of Data

PUT

GET

40H

Address register

10 bits

Peripheral

Address

Name

Peripheral Hardware

Peripheral

Address

Name

Peripheral Hardware

Effective Bit

Length

Effective Bit

Length

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