NEC PD78P214 Manuale Utente
43
Chapter 3 CPU Function
3
3.1.2 Internal RAM Area
A 512-byte (384-byte for the
µPD78212) general-purpose static RAM is incorporated into the area from 0FD00H to
0FEFFH.
This area consists of the following two RAMs:
°
Peripheral RAM (PRAM)
: 0FD00H to 0FDFFH (0FD80H to 0FDFFH for the
µPD78212)
°
Internal dual-port RAM (IRAM): 0FE00H to 0FEFFH
The internal dual-port RAM (IRAM) can be accessed at high speed.
Short direct addressing mode for high-speed access can be used for the area from 0FE20H to 0FEFFH. (Refer to
Chapter 6, Instruction, “78K/II Series User’s Manual.”)
Chapter 6, Instruction, “78K/II Series User’s Manual.”)
General-purpose registers of four banks are mapped into the 32-byte area from 0FEE0H to 0FEFFH. Macro service
control words are mapped into the 30-byte area from 0FEC2H to 0FEDFH.
control words are mapped into the 30-byte area from 0FEC2H to 0FEDFH.
Caution Program fetch from the internal RAM area is prohibited.
Remark It is convenient to store data, work areas, and status flags that are frequently accessed in the area from 0FE20H to 0FEC1H. The area
from 0FE00H to 0FE1FH can be accessed at high speed. If this area is used as a stack area, macro service channel, or a data transfer
area for a macro service, system throughput can be improved. (For this area, short direct addressing cannot be used. This area is
addressed in the same way as other memory spaces. The area, however, can be accessed faster than other memory spaces. In terms
of the efficiency of the entire system, it is advantageous to use the area as a stack area, macro service channel, or a data transfer area
for a macro service channel.)
area for a macro service, system throughput can be improved. (For this area, short direct addressing cannot be used. This area is
addressed in the same way as other memory spaces. The area, however, can be accessed faster than other memory spaces. In terms
of the efficiency of the entire system, it is advantageous to use the area as a stack area, macro service channel, or a data transfer area
for a macro service channel.)
3.1.3 Special Function Register (SFR) Area
Special function registers (SFR), which are on-chip hardware peripherals, are mapped into the area from 0FF00H
to 0FFFFH (see Section 3.2.5).
to 0FFFFH (see Section 3.2.5).
The area from 0FFD0H to 0FFDFH is mapped as an external SFR area. This area allows the
µPD78214 in external
memory expansion mode (selected by memory expansion mode register MM) and
µPD78213 (ROM-less) to access
external peripheral I/O.
Caution Never access an address to which no SFR is mapped in this area. If this is attempted, the
µ
PD78214 may enter a deadlock. To restore
the device from the deadlock, a reset signal must be input.
3.1.4 External SFR Area
In the SFR area, the 16-byte area from 0FFD0H to 0FFDFH is mapped as an external SFR area. This area allows the
µPD78214 in external memory expansion mode (selected by memory expansion mode register MM) and the
µPD78214 in external memory expansion mode (selected by memory expansion mode register MM) and the
µPD78213 (ROM-less) to access external peripheral I/O through the address bus or address/data bus.
The external SFR area can be accessed by the SFR addressing method. The area features the following: Peripheral
I/O can be easily manipulated and the object size can be compressed. This area can also be specified as an SFR
of macro service type B.
The external SFR area can be accessed by the SFR addressing method. The area features the following: Peripheral
I/O can be easily manipulated and the object size can be compressed. This area can also be specified as an SFR
of macro service type B.
When the external SFR area is accessed, the bus operates as in ordinary memory access (see Chapter 13).
3.1.5 External Memory Space
The area from 04000H to 0FCFFH (02000H to 0FD7FH for the
µPD78212) is an external memory space that can be
accessed by setting a memory expansion mode register (MM). In this area, programs and table data can be stored
and peripheral I/O devices can be mapped.
and peripheral I/O devices can be mapped.
For the
µPD78213, the area from 00000H to 0FCFFH can be accessed at any time.
3.1.6 External Extension Data Memory Space
The area from 10000H to FFFFFH can be accessed if 1M-byte expansion mode is selected by the memory expansion
mode register (MM). In this mode, pins P60 to P63 of port 6 function as the expansion address bus of four bits (A16
to A19). The data memory space is manipulated as 16 banks of 64K bytes. The low-order four bits of registers P6
and PM6 function as a bank register for selecting a bank. This memory space is useful if the kanji character
generator or a large amount of data is used.
mode register (MM). In this mode, pins P60 to P63 of port 6 function as the expansion address bus of four bits (A16
to A19). The data memory space is manipulated as 16 banks of 64K bytes. The low-order four bits of registers P6
and PM6 function as a bank register for selecting a bank. This memory space is useful if the kanji character
generator or a large amount of data is used.