Rainbow Electronics AT89C5131 - Manual (Page 51)

51
AT89C5131
4136A–USB–03/03
EEPROM Data Memory
Description The 1-Kbyte on-chip EEPROM memory block is located at addresses 0000h to 03FFh of
the XRAM memory space and is selected by setting control bits in the EECON register.
A read in the EEPROM memory is done with a MOVX instruction.
A physical write in the EEPROM memory is done in two steps: write data in the column
latches and transfer of all data latches into an EEPROM memory row (programming).
The number of data written on the page may vary from 1 to 128 bytes (the page size).
When programming, only the data written in the column latch is programmed and a ninth
bit is used to obtain this feature. This provides the capability to program the whole mem-
ory by bytes, by page or by a number of bytes in a page. Indeed, each ninth bit is set
when the writing the corresponding byte in a row and all these ninth bits are reset after
the writing of the complete EEPROM row.
Write Data in the Column
Latches Data is written by byte to the column latches as for an external RAM memory. Out of the
11 address bits of the data pointer, the 4 MSBs are used for page selection (row) and 7
are used for byte selection. Between two EEPROM programming sessions, all the
addresses in the column latches must stay on the same page, meaning that the 4 MSB
must not be changed.
The following procedure is used to write to the column latches:
• Set bit EEE of EECON register
• Stretch the MOVX to accommodate the slow access time of the column latch (Set
bit M0 of AUXR register)
• Load DPTR with the address to write
• Store A register with the data to be written
• Execute a MOVX @DPTR, A
• If needed, loop the three last instructions until the end of a 128 bytes page
Programming The EEPROM programming consists on the following actions:
• Writing one or more bytes of one page in the column latches. Normally, all bytes
must belong to the same page; if not, the first page address will be latched and the
others discarded.
• Launching programming by writing the control sequence (54h followed by A4h) to
the EECON register.
• EEBUSY flag in EECON is then set by hardware to indicate that programming is in
progress and that the EEPROM segment is not available for reading.
• The end of programming is indicated by a hardware clear of the EEBUSY flag.
Read Data The following procedure is used to read the data stored in the EEPROM memory:
• Set bit EEE of EECON register
• Stretch the MOVX to accommodate the slow access time of the column latch (Set
bit M0 of AUXR register)
• Load DPTR with the address to read
• Execute a MOVX A, @DPTR