ST6285B datasheet(13/78 Pages) STMICROELECTRONICS

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ST62T85B/E85B

MEMORY MAP (Cont’d)

1.3.6 Data RAM/EEPROM and LCD RAM Bank

Address: CBh

—

Write only

Bit 7 = This bit is not used

Bit 6 - DRBR6. This bit, when set, selects LCD

RAM Page 2.

Bit 5 - DRBR5. This bit, when set, selects LCD

RAM Page 1.

Bit 4 - DRBR4. This bit, when set, selects RAM

Page 2.

Bit 3 - DRBR3. This bit, when set, selects RAM

Page 1.

Bit2. These bits are not used.

Bit 1 - DRBR1. This bit, when set, selects

EEPROM Page 1.

Bit 0 - DRBR0. This bit, when set, selects

EEPROM Page 0.

The selection of the bank is made by programming

the Data RAM Bank Switch register (DRBR regis-

ter) located at address CBh of the Data Space ac-

cording to Table 1. No more than one bank should

be set at a time.

The DRBR register can be addressed like a RAM

Data Space at the address CBh; nevertheless it is

a write only register that cannot be accessed with

single-bit operations. This register is used to select

the desired 64-byte RAM/EEPROM bank of the

Data Space. The number of banks has to be load-

ed in the DRBR register and the instruction has to

point to the selected location as if it was in bank 0

(from 00h address to 3Fh address).

This register is not cleared during the MCU initiali-

zation, therefore it must be written before the first

access to the Data Space bank region. Refer to

the Data Space description for additional informa-

tion. The DRBR register is not modified when an

interrupt or a subroutine occurs.

Notes :

Care is required when handling the DRBR register

as it is write only. For this reason, it is not allowed

to change the DRBR contents while executing in-

terrupt service routine, as the service routine can-

not save and then restore its previous content. If it

is impossible to avoid the writing of this register in

interrupt service routine, an image of this register

must be saved in a RAM location, and each time

the program writes to DRBR it must write also to

the image register. The image register must be

written first, so if an interrupt occurs between the

two instructions the DRBR is not affected.

In DRBR Register, only 1 bit must be set. Other-

wise two or more pages are enabled in parallel,

producing errors.

Table 5. Data RAM Bank Register Set-up

DRBR6

DRBR5

DRBR4

DRBR3

DRBR1

DRBR0

DRBR

ST62T85B/E85B

None

EEPROM Page 0

EEPROM Page 1

RAM Page 1

10h

RAM Page 2

20h

LCD RAM Page 1

40h

LCD RAM Page 2

other

Reserved

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