NEC PD17062 - Manual (Page 35)

35
µ
PD17062
5.2.1 Function of System Register (SYSREG)
The system register is used to control the CPU.
For example, the bank register shown in Fig. 5-2 is used to specify a data memory bank, while the general-
purpose register pointer specifies the row address of the general-purpose register.
See Chapter 8 for details.
5.2.2 Function of General-Purpose Register (GR)
The general-purpose register can be used both to perform operations on the data in data memory and to
transfer data to and from data memory.
The bank and the row address for the general-purpose register are specified by the general-purpose register
pointer in the system register. The general-purpose register pointer of the
µ
PD17062 always specifies BANK0.
For example, if the general-purpose register pointer is set to 0, 16 nibbles at row address 0 of BANK0, or
addresses 00H to 0FH of BANK0, are allocated as the general-purpose register.
Note that if the general-purpose register is used, transfer and arithmetic/logical instructions that involve
the general-purpose register and immediate data cannot be executed. That is, the execution of a transfer or
an arithmetic/logical instruction that involves the general-purpose register and immediate data requires that
the general-purpose register be treated as data memory.
For example, assume that row address 0H of BANK0 is allocated as the general-purpose register (i.e., the
value of the general-purpose register pointer is 0). In this case, if the currently selected bank is BANK0 (i.e.,
the value of the bank register is 0), executing ADD 00H, #1 increments by 1 the contents of address 00H of
BANK0, which is allocated as the general register. However, if the currently selected bank is BANK1 (i.e., the
value of the bank register is 1), executing ADD 00H, #1 increments by 1 the contents of address 00H of BANK1.
See Chapter 6 for details.
5.2.3 Data Buffer (DBF)
The data buffer is used to store data to be transferred to a peripheral circuit, such as the reference voltage
setting data for an A/D converter. It is also used to store data transferred from a peripheral circuit, such as
input data for a serial interface.
See Chapter 10 for details.
5.2.4 General-Purpose Port Data Registers (port registers)
Port registers are used both to store output data for general-purpose I/O ports and to read input data. The
output of the pins assigned as an output port is determined by storing data into the port registers that
correspond to those pins. The input status of those pins assigned as an input port can be detected by reading
the contents of the port registers corresponding to those pins. Fig. 5-6 shows the correspondence between
the port registers and ports (pins).
See Chapter 15 for details.