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8XC196NP, 80C196NU USER’S MANUAL
5-24
For nonextended instructions, the EP_REG register provides the page number. Data and constants
in this page are called near data and near constants.
in this page are called near data and near constants.
NOTE
The 8XC196NP allows you to change the value of EP_REG to control which
memory page a nonextended instruction accesses. However, software tools
require that EP_REG be equal to 00H. The 80C196NU forces all nonextended
data accesses to page 00H. You cannot use EP_REG to change pages.
memory page a nonextended instruction accesses. However, software tools
require that EP_REG be equal to 00H. The 80C196NU forces all nonextended
data accesses to page 00H. You cannot use EP_REG to change pages.
Data outside the page specified by EP_REG is called far data. To access far data, you must use
extended instructions. For extended instructions, the CPU provides the page number.
extended instructions. For extended instructions, the CPU provides the page number.
Figure 5-8. Formation of Extended and Nonextended Addresses
The code example below illustrates the use of extended instructions to access data in page 01H.
EP_REG
EQU 1FE5H
RSEG AT 1CH
RSEG AT 1CH
TEMP:
DSW 1
RESULT:
DSW 1
CSEG AT 0FF2080H
.
CSEG AT 0FF2080H
.
;some code
.
;
.
;
SUBB:
PUSHA
;save flags, disable interrupts
LD
TEMP,#1234H
;
EST
TEMP,010600H
;store temp value in 010600H
ADD
RESULT,TEMP,#4000H
;do something with registers
EST
RESULT,010602H
;store result in 010602H
.
;more eld/est instructions
.
;
.
;
POPA
;restore flags and interrupts
RET
;
.
;more code
.
;
.
;
DONE:
BR DONE
END
END
A2514-01
From CPU
16-bit Data Address Register
23
16 15
0
From EP_REG
16-bit Data Address Register
23
16 15
0
Nonextended Address
Extended Address