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CHAPTER 5 DATA MEMORY (RAM)
32
5.1.1 System Register (SYSREG)
The system register (SYSREG) consists of the 12 nibbles allocated at addresses 74H to 7FH in data memory. The
system register (SYSREG) is allocated independently of the banks. This means that each bank has the same system
register at addresses 74H to 7FH.
Figure 5-2 shows the configuration of the system register.
Figure 5-2. System Register Configuration
System Register (SYSREG)
Address
74H
75H
76H
77H
78H
79H
7AH
7BH
7CH
7DH
7EH
7FH
Index register
(IX)
Data memory
row address
pointer (MP)
Name
(Symbol)
Address register
(AR)
Window
register
(WR)
Bank
register
(BANK)
General
register
pointer (RP)
Program
status word
(PSWORD)
5.1.2 Data Buffer (DBF)
The data buffer consists of four nibbles allocated at addresses 0CH to 0FH in BANK0 of data memory. Figure
5-3 shows the configuration of the data buffer.
Figure 5-3. Data Buffer Configuration
Data Buffer (DBF)
Address
0CH
0DH
0EH
0FH
Symbol
DBF3
DBF2
DBF1
DBF0
5.1.3 General Register (GR)
The general register consists of 16 nibbles specified by an arbitrary row address in a bank in data memory.
This arbitrary row address in a bank is pointed to by the register pointer (RP) in the system register (SYSREG).
In the case of the
µ
PD17120 and 17121, addresses 40H to 6EH are non-mounted areas. These areas should not
be specified as a general register.
Figure 5-4 shows the configuration of the general register (GR).
Summary of Contents for mPD17120 Subseries
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