Octagon PC-500, Руководство пользователя

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18-1
PC-500 user’s manual Serial EEPROM and CMOS RAM
Chapter 18:
Serial EEPROM and CMOS RAM
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Description
Up to 768 words of user-definable data can be saved in the serial
EEPROM. The serial EEPROM does not require battery backup to
maintain the data when the system power is off. The serial EEPROM is
easily accessible via software interrupts by most programming
languages.
The calendar/clock provides the user with 128 bytes of user-defined
CMOS RAM. This RAM requires battery backup to maintain data. If a
battery is not desirable, this data can be stored in serial EEPROM,
written to CMOS RAM on powerup, changed and written back to serial
EEPROM.
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Enhanced INT 17h function definitions
This section provides definitions for both serial EEPROM and CMOS
RAM functions. The serial EEPROM definitions include the following
functions: Read a single word from serial EEPROM, Write a single word
to serial EEPROM, Read multiple words from serial EEPROM, Write
multiple words to serial EEPROM, and Return serial EEPROM size.
The CMOS RAM definitions include the following functions: Read ex-
tended CMOS RAM, Write extended CMOS RAM, Check CMOS battery,
Copy contents of serial EEPROM to extended CMOS RAM, and Copy
contents of extended CMOS RAM to serial EEPROM.
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Serial EEPROM
Read a single word from the serial EEPROM
Function: fch
Subfunction: 00h
Purpose: To read a single word from the on-board serial
EEPROM.
Calling registers: AH fch
AL 00h
BX Word address (zero based)
DX ffffh (relative to user area)