Rainbow Electronics T89C51CC02 - Manual (Page 32)

32 Rev.A - May 17, 2001
Preliminary
T89C51CC02
9. EEPROM data memory
9.1. General description
The 2k byte on-chip EEPROM memory block is located at addresses 0000h to 07FFh of the ERAM 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 memory 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.
9.2. Write Data in the column latches
Data is written by byte to the column latches as for an ERAM 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 no 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
•
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
9.3. 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.