TP3420A Datasheet, PDF(29/32 Page) National Semiconductor (TI)

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TP3420A Datasheet, PDF (29/32 Pages) National Semiconductor (TI) – ISDN S/T Interface Device

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is checked to see if it contains new data; if yes the data is

sent out from the MFT1H FIFO, if not, then the data from the

MFT1L register is sent.

If both the buffers are full, then a third load to the MFT1H

second and the second buffer to be loaded with the third

load. This way if a DTSE and FECV are already loaded, and

the power on the NT1 starts to fail, the software can still write

a LP command in the MFT1H register as well as the MFT1L

the earliest moment and will continue until the power is com-

pletely lost.

Whenever a MFT1H command is written, a software flag

FL__EXT (extend SC1L) should be set. This flag informs the

software that 1 occurrence of the present 6x repetition of the

SC1L messages was overwritten by a message from SC1H,

and hence it is necessary to extend the MFT1L command for

another 30 ms to guarantee 6x tranmission. This flag is reset

after the next 30 ms tick.

SC1 Messaging Sequence

Example

Assume Software flags and buffers are defined as:

SC1L__PB - software variable, indicating previous data sent

via the SC1L channel

SC1L__NB - software variable, indicating the next value to

be sent via the SC1L channel

FL__EXT - Flag to Extend SC1L command for another 30

ms.

MFT1L, MFT1H and MFT2, are the device registers.

The sequences of events shown below indicate activity on

the SC1 channel on the line and the actions required by the

local microcontroller at each 30 ms (MFC status interrupt)

ticks.

Time

(ms)

0 (MFC INT)

SC1

I430 Frame Content

(IDLE)

(LRS)

(DTSE)

(LRS)

(FECV)

(LRS)

(DTSE)

(FECV)

(LRS)

Actions Required

if FL__EXT flag not set, check for new flags on SC1L, assume LRS.

Check for SC2 channel. Send SC2 command > MFT2.

SC1__NB(IDLE)> SC1__PD, SC1 command(LRS) > SC1__NB,

SC1__NB(LRS) > MFT1L.

if FL__EXT flag not set, check for new flags on SC1L, assume IDLE.

Check for SC2 channel Flags. Send SC2 command as appropriate.

SC1__NB(LRS)> SC1__PB, SC1L command(IDLE) > SC1__NB,

SC1__NB > MFT1L(IDLE).

Assume DTSE-IN Interrupt from UID, Send DTSE > MFT1H register.

Set the FL__EXT. SC1L__PB > MFT1L (LRS).

RMFE in Interrupt from local SID, FECV > MFT1H,

SC1L__PB > MFT1L(LRS). Set FL-EXT.

if FL__EXT flag set, do not check for new flags on SC1L, but check for

SC2 channel. Reset FL__EXT. Send SC2 command as appropriate,

SC1L__NB (IDLE) > MFT1L.

DTSE-IN Interrupt from UID, DTSE > MFT1H register. Set

FL__EXT, SC1L__PB > MFT1L register.

Also RMFE in Interrupt from local SID, FECV > MFT1H register. Set

FL__EXT. SC1L__PB > MFT1L register.

Now the FECV command is queued in the MFT1H register.

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