CHAPTER 7 SYSTEM REGISTER (SYSREG)
47
7.5 INDEX REGISTER (IX) AND DATA MEMORY ROW ADDRESS POINTER (Memory Pointer: MP)
7.5.1 Index Register (IX)
IX is used for address modification to data memory. It differs from MP in that its modification object is an address
that is specified as the bank or operand m.
As shown in Figure 7-7, IX is mapped to a total of 12 bits of system registers: 7AH (IXH), 7BH (IXM), and 7CH
(IXL). The index register enable flag (IXE) which enables address modification by IX is allocated to the lowest bit
of the PSW.
When IXE=1, an address in data memory specified with operand m is not m but the address indicated by the OR
of m, IXM and IXL. The bank specified at this time is that indicated by the OR of BANK and IXH.
Remark
The IXH of the
µ
PD17120 subseries is "fixed to 0" and therefore the bank is modified even when IXE=1
(thus preventing the bank from becoming other than 0).
7.5.2 Data Memory Row Address Pointer (Memory Pointer: MP)
MP is used for address modification to data memory. It differs from IX in that its modification object is the row
address of the address that is indirectly specified with the bank and operand @r.
As shown in Figure 7-7, MPH and IXH, and MPL and IXM, are respectively mapped to the same addresses (system
registers 7AH and 7BH). It is MPH's lower 3 bits and MPL's full 7 bits that are actually functioning as the MP. To
MPH's most significant bit is allocated the memory pointer enable flag (MPE) which enables address modification
by the MP.
When MPE=1, the bank and row address of the data memory indirectly specified with operand @r is not BANK
and m
R
but the address specified by the MP. (The column address is specified with the contents of r regardless
of the MPE.) At this time, MPH's lower 3 bits and MPL's most significant 4 bits point to BANK; and MPL's lower
3 bits point to the row address.
Remark
The MPH's lower 3 bits and MPL's most significant bit in the
µ
PD17120 subseries are "fixed to 0" and
therefore the bank is cleared to 0 even when MPE=1 (thus preventing the bank from becoming other
than 0).
Summary of Contents for mPD17120 Subseries
Page 15: ... x MEMO ...
Page 23: ... MEMO 8 ...
Page 45: ... MEMO 30 ...
Page 49: ... MEMO 34 ...
Page 55: ... MEMO 40 ...
Page 93: ... MEMO 78 ...
Page 99: ... MEMO 84 ...
Page 102: ...CHAPTER 11 ARITHMETIC AND LOGIC UNIT 87 MEMO ...
Page 119: ... MEMO 104 ...
Page 175: ... MEMO 160 ...
Page 199: ... MEMO 184 ...
Page 265: ... MEMO 250 ...
Page 281: ...266 MEMO ...
Page 285: ... MEMO 270 ...
Page 289: ... MEMO 274 ...