STLC5411FN datasheet(22/72 Pages) STMICROELECTRONICS

22 / 72 page

Monitor channel

The Monitor channel is used to write and read all

STLC5411 internal registers. Protocol on the

Monitor channel allows a bidirectional transfer of

bytes between UID and a control unit with ac-

knowledgement at each received byte. Bytes are

transmitted on the Br output and received on the

Bx input in the Monitor channel time slot.

A write or read cycle is always constituted of two

bytes.(see fig. 5). It is possible to operate several

write or read cycles within a single monitor mes-

sage.

Note: Special format is used for EOC channel.

Write cycle

The format to write a message into the UID is:

1st byte

2nd byte

A7-A1:

A0:

D7-D0:

Write/Read back Indicator

After the first byte is shifted in, Register address

is decoded. A0 set low indicates a write cycle: the

content of the following received byte has to be

loaded into the addressed register.

A0 set high indicates a read-back cycle request.

the second byte content is not significative.

STLC5411 will respond to the request by sending

back a message with the register content associ-

ated with its own address. It is then possible for

the microprocessor to receive the required regis-

ter content after several other pending messages.

To avoid any loss of data, it is recommended to

operate only one read-back request at a time.

Note: Special format is used for EOC channel.

Read cycle

When UID has a register content to send to the

controller, it send it on the monitor channel di-

rectly. Note that the data to send can be the con-

tent of a Register previously requested by the

controller by means of a read-back request.

The format of the message sent by the UID is:

1st byte

2nd byte

A7-A1:

A0:

D7-D0:

forced to 0 is spontaneous

interrupt, forced to 1 if read-

back

Exchange Protocol

STLC5411 validates a received byte if it is de-

tected two consecutive times identical. (see fig. 5)

The exchange protocol is identical for both direc-

tions. The sender uses the E bit to indicate that it

is sending a Monitor byte while the receiver uses

A bit to acknowledge the received byte.When no

message is transferred, E bit and A bit are forced

to inactive state.

A transmission is started by the sender (Transmit

section of the Monitor channel protocol handler)

by putting the E bit from inactive to active state

and by sending the first byte on Monitor channel

in the same frame. Transmission of a message is

allowed only if A bit sent from the receiver has

been set inactive for at least two consecutive

frames. When the receiver is ready, it validates

the incoming byte when received identical in two

consecutive frames. Then, the receiver set A bit

from the inactive to the active state (preacknowl-

edgement) and maintain active at least in the fol-

lowing frame (acknowledgement).

If validation is not possible (two last bytes re-

ceived are not identical) the receiver aborts the

message by setting the A bit active for only a sin-

gle frame.The second byte can be transmitted by

the sender putting the E bit from the active to the

inactive state and sending the second byte on the

Monitor channel in the same frame . The E bit is

set inactive for only one frame. If it remains inac-

tive more than one frame, it is an end of mes-

sage. The second byte may be transmitted only

after receiving of the pre-acknowledgement of the

previous byte . Each byte has to be transmitted at

least in two consecutive frames.

The receiver validates the current received byte

as for the first one and then set the A bit in the

next two frames first from the active state to the

inactive state (pre-acknowledgement) and back to

the active (acknowledgement). If the receiver can-

not validates the received current byte (two bytes

received not identical)it pre-acknowledges nor-

mally but let the A bit in the inactive state in the

next frame which indicates an abort request . If a

message sent by the UID is aborted, the UID will

send again the complete message until receiving

of an acknowledgement . A message received by

the UID can be acknowledged or aborted with

flow Control.

The most significant bit (MSB) of Monitor byte is

sent first on the Monitor channel. E & A bits are

active low and inactive state on Br is 5 V. When

no byte is transmitted, Monitor channel time slot

STLC5411

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