MEMORY PARTITIONS

Table 4-8. Selecting a Window of the Upper Register File

Register RAM	WSR or WSR1 Value	WSR or WSR1 Value	WSR Value
Locations	for 32-byte Window	for 64-byte Window	for 128-byte Window
(Hex)	(00E0–00FFH or 0060–007FH)	(00C0–00FFH or 0040–007FH)	(0080–00FFH)
03E0–03FF	5FH
03C0–03DF	5EH	2FH
03A0–03BF	5DH
0380–039F	5CH	2EH	17H
0360–037F	5BH
0340–035F	5AH	2DH
0320–033F	59H
0300–031F	58H	2CH	16H
02E0–02FF	57H
02C0–02DF	56H	2BH
02A0–02BF	55H
0280–029F	54H	2AH	15H
0260–027F	53H
0240–025F	52H	29H
0220–023F	51H
0200–021F	50H	28H	14H
01E0–01FF	4FH
01C0–01DF	4EH	27H
01A0–01BF	4DH
0180–019F	4CH	26H	13H
0160–017F	4BH
0140–015F	4AH	25H
0120–013F	49H
0100–011F	48H	24H	12H

4.3.2Addressing a Location Through a Window

After you have selected the desired window, you need to know the direct address of the memory location (the address in the lower register file). For SFRs, refer to the WSR tables in Appendix

C.For register file locations, calculate the direct address as follows:

1.Subtract the base address of the area to be remapped (from Table 4-8) from the address of the desired location. This gives you the offset of that particular location.

2.Add the offset to the base address of the window (from Table 4-9). The result is the direct address.

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Table 4-9. Windowed Base Addresses

	Window Size	WSR Windowed Base Address	WSR1 Windowed Base Address
		(Base Address in Lower Register File)	(Base Address in Lower Register File)
	32-byte	00E0H	0060H
	64-byte	00C0H	0040H
	128-byte	0080H	—

Appendix C includes a table of the windowable SFRs with the window selection register values and direct addresses for each window size. The following examples explain how to determine the WSR value and direct address for any windowable location. An additional example shows how to set up a window by using the linker locator.

4.3.2.132-byte Windowing Example

Assume that you wish to access location 014BH (a location in the upper register file used for gen- eral-purpose register RAM) with direct addressing through a 32-byte window. Table 4-8 on page 4-21 shows that you need to write 4AH to the window selection register. It also shows that the base address of the 32-byte memory area is 0140H. To determine the offset, subtract that base address from the address to be accessed (014BH – 0140H = 000BH). Add the offset to the base address of the window in the lower register file (from Table 4-9). The direct address is 00EBH (000BH + 00E0H) for a WSR window or 006BH (000BH + 0060H) for a WSR1 window.

4.3.2.264-byte Windowing Example

Assume that you wish to access the SFR at location 1F8CH with direct addressing through a 64byte window. Table 4-8 on page 4-21 shows that you need to write 3EH to the window selection register. It also shows that the base address of the 64-byte memory area is 1F80H. To determine the offset, subtract that base address from the address to be accessed (1F8CH – 1F80H = 000CH). Add the offset to the base address of the window in the lower register file (from Table 4-9). The direct address is 00CCH (000CH + 00C0H) for a WSR window or 004CH (000CH + 0040H) for a WSR1 window.

4.3.2.3128-byte Windowing Example

Assume that you wish to access the SFR at location 1F82H with direct addressing through a 128byte window. Table 4-8 on page 4-21 shows that you need to write 1FH to the window selection register. It also shows that the base address of the 128-byte memory area is 1F80H. To determine the offset, subtract that base address from the address to be accessed (1F82H – 1F80H = 0002H). Add the offset to the base address of the window in the lower register file (from Table 4-9). The direct address is 0082H (0002H + 0080H).

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4.3.2.4Unsupported Locations Windowing Example

Assume that you wish to access location 1FE7H (the EP_PIN register, a memory-mapped SFR) with direct addressing through a 128-byte window. This location is in the range of addresses (1FE0–1FFFH) that cannot be accessed through windows. Although you could set up the window by writing 1FH to the WSR, reading this location through the window would return FFH (all ones) and writing to it would not change the contents. However, you could directly address the remaining SFRs in the range of 1F80–1FDFH.

4.3.2.5Using the Linker Locator to Set Up a Window

In this example, the linker locator is used to set up a window. The linker locator locates the window in the upper register file and determines the value to load in the WSR for access to that window. (Please consult the manual provided with the linker locator for details.)

*********			mod1	**************
mod1	module main				;Main module for linker
public function1
extrn	?WSR				;Must declare ?WSR as external
wsr	equ		14h:byte
sp	equ		18h:word
oseg
	var1:		dsw	1	;Allocate variables in an overlayable segment
	var2:		dsw	1
	var3:		dsw	1
cseg
function1:
	push		wsr		;Prolog code for wsr
	ldb		wsr, #?WSR		;Prolog code for wsr
	add	var1, var2, var3			;Use the variables as registers
	;
	;
	;
	ldb		wsr, [sp]		;Epilog code for wsr
	add	sp, #2			;Epilog code for wsr
	ret
end
********			mod2	**************

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public function2 extrn ?WSR

wsr	equ	14h:byte
sp	equ	18h:word
oseg
	var1:	dsw	1
	var2:	dsw	1
	var3:	dsw	1
cseg
function2:
	push	wsr		;Prolog code for wsr
	ldb	wsr, #?WSR		;Prolog code for wsr
	add var1, var2, var3
	;
	;
	;
	ldb	wsr, [sp]		;Epilog code for wsr
	add sp, #2			;Epilog code for wsr
	ret
end
******************************

The following is an example of a linker invocation to link and locate the modules and to determine the proper windowing.

RL196 MOD1.OBJ, MOD2.OBJ registers(100h-03ffh) windowsize(32)

The above linker controls tell the linker to use registers 0100–03FFH for windowing and to use a window size of 32 bytes. (These two controls enable windowing.)

The following is the map listing for the resultant output module (MOD1 by default):

SEGMENT MAP FOR mod1(MOD1):

TYPE	BASE	LENGTH	ALIGNMENT	MODULE NAME
----	----	------	---------	-----------
**RESERVED*	0000H	001AH
STACK	001AH	0006H	WORD
*** GAP ***	0020H	00E0H
OVRLY	0100H	0006H	WORD	MOD2
OVRLY	0106H	0006H	WORD	MOD1
*** GAP ***	010CH	1F74H
CODE	2080H	0011H	BYTE	MOD2
CODE	2091H	0011H	BYTE	MOD1
*** GAP ***	20A2H	DF5EH

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