3 data buffer and table referencing – NEC PD17062 User Manual
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PD17062
10.3 DATA BUFFER AND TABLE REFERENCING
10.3.1 Table Referencing
Tables are referenced by reading the constant data from program memory into the data buffer. This is done
using the MOVT DBF, @AR instruction.
Therefore, if display data or other constant data is written to program memory in advance and a table
reference instruction is executed, writing of a complex data conversion program is unnecessary.
The MOVT instruction is described below.
A example program is given in Section 10.3.2.
MOVT DBF, @AR ; Reads the contents of the program memory addressed by the address register into the
data buffer as shown below.
When a table reference instruction is executed, the stack is used one level.
Because the address register (AR) has only eight valid bits, program memory available for table reference
is limited to 256 steps from address 0000H to address 00FFH.
See also Chapter 4 and Section 8.1.
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MOVT DBF, @ AR
DBF3
DBF2
DBF1
DBF0
b
15
b
14
b
13
b
12
b
11
b
10
b
9
b
8
b
7
b
6
b
5
b
4
b
3
b
2
b
1
b
0
b
15
b
14
b
13
b
12
b
11
b
10
b
9
b
8
b
7
b
6
b
5
b
4
b
3
b
2
b
1
b
0
Constant data
Data buffer
Program memory
(ROM)
Specifies the program memory address