ST92195C datasheet(91/249 Pages) STMICROELECTRONICS

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ST92195C/D - TELETEXT DISPLAY STORAGE RAM INTERFACE

TDSRAM (Cont’d)

7.3.4 Register Description

7.3.4.1 Data Registers

BUF0..15 R240 .. R255 Page 36Read/Write

RAM Buffer Data Register x = 0,..,15

BUF16..31 R240 .. R255 Page 37 Read/Write

RAM Buffer Data Register x = 16,..,31

BUF32..39 R240 .. R247Page 38 Read/Write

RAM Buffer Data Register x = 32,..,39

Reset Value: xxxx xxxx (xxh)

Bits 7:0 = BUFx[7:0]: presents the x-th byte

(MSB...LSB) of the 40 byte data buffer belonging

to the teletext function. The data registers are not

accessible during the transfer (BUSY = “1”). A

buffer exchange starts with BUF0 and ends with

BUF39 whether the address is incremented or

decremented.

7.3.4.2 Address Registers

MULTI-BYTE TRANSFER START ADDRESS

R250 - Read/Write

Reset Value: 1000 0000 (80h)

Bits 7:6 = Hard wired to map correctly into the

memory space, defined for the RAM.

Bit 5 = SA[13]: This bit must always be written to

Bits 4:0 = SA[12:8]: Bit13..bit8 of the 13-bit start

address for the 40-byte data transfer have to be

written into this register.

MULTI-BYTE TRANSFER START ADDRESS

R251 - Read/Write

Reset Value: 0000 0000 (00h)

Bits 7:0 = SA[7:0]: Bit7..bit0 of the 13-bit start ad-

dress for the 40-byte data transfer have to be writ-

ten into this register.

MBTSA1..MBTSA0 are not accessible during the

transfer (BUSY = ”1”).

MBTSA is used as a counter to generate the TD-

SRAM (R/W) address. When the Multi-Byte Trans-

fer is done, this register is incremented or decre-

mented by 40 depending on the BADU bit in the

BUFC register R248 page 26h.

The normal mode corresponds to a counter incre-

mentation.

When the user wants to use decrementation mode

(using the BADU bit), the address must be com-

plemented before writing to the 13 LSB of

MBTSA1.. MBTSA0.

For example, to decrement the counter from the

address:

– SA12 SA11........ SA0 = 1 0101 0101 0101b =

1555h,

the software must load:

– SA12n SA11n........ SA0n = 0 1010 1010 1010b

= 0AAAh,

in the start address register. The BADU bit must

be set to 1.

The value read in this case will be MBTSA1..

MBTSA0 = 8AAAh (The 3 MSB are hard wired).

BUFx.7 BUFx.6 BUFx.5 BUFx.4 BUFx.3 BUFx.2 BUFx.1 BUFx.0

SA13 SA12 SA11 SA10

SA9

SA8

SA7

SA6

SA5

SA4

SA3

SA2

SA1

SA0

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