COP8SCR9KMT7 datasheet(20/80 Pages) NSC

20 / 80 page

10.0 Functional Description

(Continued)

Figure 7 illustrates how the S register data memory exten-

sion is used in extending the lower half of the base address

range (00 to 7F hex) into 256 data segments of 128 bytes

each, with a total addressing range of 32 kbytes from XX00

to XX7F. This organization allows a total of 256 data seg-

ments of 128 bytes each with an additional upper base

segment of 128 bytes. Furthermore, all addressing modes

are available for all data segments. The S register must be

changed under program control to move from one data

segment (128 bytes) to another. However, the upper base

segment (containing the 16 memory registers, I/O registers,

control registers, etc.) is always available regardless of the

contents of the S register, since the upper base segment

(address range 0080 to 00FF) is independent of data seg-

ment extension.

The instructions that utilize the stack pointer (SP) always

reference the stack as part of the base segment (Segment

0), regardless of the contents of the S register. The S register

is not changed by these instructions. Consequently, the

stack (used with subroutine linkage and interrupts) is always

located in the base segment. The stack pointer will be initial-

ized to point at data memory location 006F as a result of

reset.

The 128 bytes of RAM contained in the base segment are

split between the lower and upper base segments. The first

112 bytes of RAM are resident from address 0000 to 006F in

the lower base segment, while the remaining 16 bytes of

RAM represent the 16 data memory registers located at

addresses 00F0 to 00FF of the upper base segment. No

RAM is located at the upper sixteen addresses (0070 to

007F) of the lower base segment.

Additional RAM beyond these initial 128 bytes, however, will

always be memory mapped in groups of 128 bytes (or less)

at the data segment address extensions (XX00 to XX7F) of

the lower base segment. The additional 892 bytes of RAM in

this device are memory mapped at address locations 0100

to 017F through 0700 to 077F hex.

10.4.1 Virtual EEPROM

The Flash memory and the User ISP functions (see Section

5.7), provide the user with the capability to use the flash

program memory to back up user defined sections of RAM.

This effectively provides the user with the same nonvolatile

data storage as EEPROM. Management, and even the

amount of memory used, are the responsibility of the user,

however the flash memory read and write functions have

been provided in the boot ROM.

One typical method of using the Virtual EEPROM feature

would be for the user to copy the data to RAM during system

initialization, periodically, and if necessary, erase the page of

Flash and copy the contents of the RAM back to the Flash.

10.5 OPTION REGISTER

The Option register, located at address 0x7FFF in the Flash

Program Memory, is used to configure the user selectable

security, WATCHDOG, and HALT options. The register can

be programmed only in external Flash Memory programming

or ISP Programming modes. Therefore, the register must be

programmed at the same time as the program memory. The

contents of the Option register shipped from the factory read

00 Hex.

10138910

FIGURE 7. RAM Organization

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