UPD17708 datasheet(66/356 Pages) NEC

66 / 356 page

µPD17704, 17705, 17707, 17708, 17709

8.2.1 Register file manipulation instructions (“PEEK WR, rf”, “POKE rf, WR”)

Data is read from or written to the register file via the window register of the system registers, by using the

following instructions.

(1) “PEEK WR, rf”

Reads data of the register file addressed by “rf” to the window register.

(2) “POKE rf, WR”

Writes the data of the window register to the register file addressed by “rf”.

8.3 Control Registers

Figure 8-3 shows the configuration of the control registers.

As shown in the figure, the control registers consist of a total of 64 nibbles (64

× 4 bits) of addresses 00H

through 3FH of the register file.

Of these 64 nibbles, however, only 53 nibbles are actually used. The remaining 11 nibbles are unused

registers and prohibited from being written or read.

Each control register has an attribute of 1 nibble that identifies four types of registers: read/write (R/W), read-

only (R), write-only (W), and read-and-reset (R&Reset) registers.

Nothing is changed even if data is written to a read-only (R and R&Reset) register.

An “undefined” value is read if a write-only (W) register is read.

Among the 4-bit data in 1 nibble, the bit fixed to “0” is always “0” when it is read, and is also “0” when it is

written.

The 11 nibbles of unused registers are undefined when their contents are read, and nothing changes even

when they are written.

Table 8-1 lists the peripheral hardware control functions of the control registers.

UPD17708 Datasheet(PDF) 66 Page - NEC