Intel 8XC196NP, 80C196NU, Microcontroller manual Formation of Extended and Nonextended Addresses

8XC196NP, 80C196NU USER’S MANUAL

For nonextended instructions, the EP_REG register provides the page number. Data and 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.

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.

	From EP_REG		16-bit Data Address Register
Nonextended Address
23		16 15	0

	From CPU	16-bit Data Address Register
Extended Address
23	16 15	0

A2514-01

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
TEMP:	DSW 1
RESULT:	DSW 1
	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

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