ST5451 datasheet(18/34 Pages) STMICROELECTRONICS

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4 - 8 - 2 - M CHANNELS INTERRUPTS EOM,

RMR, XMR, RAB

Receive Direction

RMR 1/2 is a bit of interrupt register ISTA 1/2

coming high to indicate the M (or M’) channel

controller has received a valid byte on receiving

channel (two identical consecutive bytes).

The microprocessor processing order is;

1. Erasing RMR 1/2 interrupt into ISTA 1/2

2. Read MONR 1/2 register.

This order can’t be inverted because, as long as

MONR isn’t read, the receive state machine is

locked in wait state, a new byte can’t be acknow-

ledged and so, a new interrupt can’t be done.

More, if MONR is read first, the receive state ma-

chine is ready for receiving a new byte and create

another interrupt. So, if the interrupt bit corre-

sponding to the previous frame isn’t erased be-

fore a new byte arrives, this byte won’t be seen

(the microprocessor won’t be informed) and the

controller will be locked waiting for MONR read.

XAB 1/2 is a bit of the interrupt register coming

high to indicate the receive controller has de-

tected an abort (two conscutive bytes not identi-

cal) as long as this interrupt isn’t erased, the re-

ceiver is locked in wait state.

EOM 1/2 is a bit of the interrupt register coming

high to indicate the receive controller has de-

tected an end of message. As long as the inter-

rupt isn’t erased, the receiver is locked in wait

state.

Transmit Direction

XMR 1/2 is a bit of the interrupt register coming

high to indicate a byte can be written into MONX.

The processing order is:

1. Erasing XMR bit

2. Writing a new byte into MONX.

If this order is inverted, the new byte will be trans-

mitted and a new XMR may be erased before be-

ing seen by the microprocessor.

RAB 1/2 is a bit of the interrupt register coming

high to indicate the remote receiver has reported

an abort detection. The processing order is:

1. Erasing RAB bit

2. Erasing XMR bit

3. Writing a new byte into MONX.

If a write operation of the new byte is done before

the RAB erasing, the byte will be lost and the

transmitter will stay waiting for it.

4 - 8 - 3 - CI CHANNEL INTERRUPTS

CIC 1/2 is a bit of ISTA 1/2 interrupt register com-

ing high to indicate a valid byte has been de-

tected by the command indicate receive control-

ler, and readable into CIR 1/2 register. The

processing order is:

1. Erasing CIC bit

2. Reading CIR register.

If this order is inverted, a next byte may be un-

seen by the microprocessor. It is recommended

to work with ”Ping Pong” protocol on CI channels,

as non flow control is done.

4 - 9 - SOFTWARE RESET PROCEDURES

4 - 9 - 1 - XRES (Transmit Direction)

XRES is a level sensitive command of CMDR

which initialize the transmit process.

- XPR interrupt bit is erased

- XDU interrupt bit is not erased (security pro-

cedure)

- All data in FIFOs are lost

- After an XRES, the microprocessor must wait

for an XPR before writing new data.

The processing order is:

- Writing a ”1” into XRES (CMDR)

- Writing a ”0” into XRES (CMDR)

- Read ISTA0 waiting XPR or enable XPR in-

terrupt

4 - 9 - 2 - RHR (Receive Direction)

RHR is a level sensitive command of CMDR,

which reinitialize the receive process.

- RME, RPF bits are erased

- RFO bit is erased

- All frames in FIFO R are lost

- If RHR is released (got down) at the time a

frame is on line, the HDLC controller waits

for a flag.

4 - 9 - 3 - M1RES, M2RES M/CI channels

MRES is a level sensitive command of CMDR

which initialize the M/CI channel protocole in both

directions.

XMR, RAB, RMR, CIC, XAB, EOM bits are

erased by MRES.

After a clock programming (bit CRS), it’s neces-

sary to put MRES bit to initialize properly the M

protocol.

ST5451

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