EF9345 datasheet(35/38 Pages) STMICROELECTRONICS

35 / 38 page

Notes on Command Execution

1. The execution of any command starts at the

trailing edge of DS when (and only when) :

- EF9345 has been selected,

- XQR has been set,

at the previous AS falling edge.

This scheme allows loading a command and its

argument in any order. For instance, a command,

once loaded, may be re-executed with new or partly

new arguments.

2. At power on, the busy state is undeterminated.

It is recommanded to load first a dummy

command with XQR = 1 before any effective

command.

3. While Busy is set, the current command is

under execution. Register access is then

restricted.

- Read STATUS is effective.

- Write COMMAND or any other register access

are ineffective.

That is to say, the microprocessor reads undeter-

mined values and may not modify a register.

- Read STATUS or write COMMAND are effective,

- Access to other registers is ineffective.

However, the previous command is aborted and

the new command execution launched (with an

initial state undetermined for registers and memory

locations handled by the aborted command).

4. Execution suspension

The execution of any command (except VRM,

VSM) is suspended during the last and first TV line

of an active row. This is because the memory bus

cannot be allocated for microprocessor access dur-

ing this 104

µs period.

This holds too for internal resource access because

on-chip data transfer uses internal data memory

bus.

IND Command (See Figure 37)

This command transfers one byte between R1 and

an internal resource. The r parameter designates

one on-chip indirect register.

Fixed Format Character Code Access :

KRF, KRG, KRL, KRC

Each of these commands is dedicated to transfer

one complete character code between DATA reg-

isters and memory. MP is exclusively used.

KRF transfers 24 bits.

KRG transfers 16 bits

KRL transfers 12 bits.

KRC transfers 8 bits.

Code packing, pointer and data structures are ex-

plained in the corresponding character code sec-

tion.

When auto-incrementation is enabled, MP is auto-

matically updated after access so as to point to the

next location. This location corresponds to the next

right position on screen. When last position (X = 39)

is accessed, LXm is set. When last position is

accessed with auto-incrementation, alarm is also

set. MP is then pointing back at the beginning of

the row : there is no automatic Y incrementation.

Variable Code Handling Commands :

KRV EXP, CMP, KRE

An overview on these commands is given in ”han-

dling the variable codes” (40 char./row section).

KRV uses R5 to point the attribute file. LXa is set

when this file is full (the last attribute pair has been

accessed).

EXP and CMP use MP and R5 in the same way as

KRV. Furthermore, R4 points to a working double

buffer. Thse two commands process a whole row

buffer and stop either at the end of the row buffer

or when the file overflows. In the last case, the

alarm bit is set.

KRE uses MP to point to a buffer and R4 to point

to a working double buffer. R5 is unused. In other

respects, KRE is identical to KRL.

For these commands, R4(5:7) hold the LSB’s block

dress of the working buffer W.

7654321

3 is given by bit 6 of R6

Figure 38

EF9345

35/38

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