TP3420AV datasheet(19/32 Pages) NSC

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Functional Description (Continued)

A 6x multiframe counter (30 ms) in the TP3420A is enabled

by the MFC6E command, and disabled with the MFC6D

command. When the counter is enabled (MFC6E), an inter-

rupt MFC is generated locally every 30 ms and internal logic

ensures that the MFT1L messages are transmitted 6 times

unless interrupted by an MFT1H message.

Alternatively, if the software chooses to keep count of repeti-

tions of transmitted multiframe messages, the command

MFC1E can be used to cause the interrupt MFC at every

multiframe boundary (5 ms). The 6x transmit logic is then

disabled. If both MFC6E and MFC1E commands are loaded,

the MFC1E command has precedence and causes the 1x

(5 ms) interrupt. It is expected that the user will prefer the

30 ms interrupt to control transmission of multiframe mes-

sages because it reduces the processor load considerably,

as outlined below and in examples in the Appendix A.

Software Table of SC1 Messages

The software in the NT should keep a table of SC1 mes-

sages to be communicated to the TE, and use the MFC (30

ms) interrupt as a synchronous timer to load SC1 messages.

Using X’3X command for SC1 messages, the software must

write the appropriate Low Priority message to the MFT1L

transmitted on the next 6x multiframe boundary and is re-

peated 6 times. If the MFT1L register is not updated by a

new MICROWIRE command from the CPU within 30 ms, the

data from the MFT1L register is re-transmitted another 6

times.

Transmission of SC1H - High Priority Messages

In the NT mode, commands such as LP, FECV, and DTSE

are considered to be High Priority messages. These are

loaded through the MFT1H register and sent out once on the

next multiframe boundary. In the following multiframe this

message gets replaced with the contents of MFT1L, the Low

Priority Register. At every multiframe boundary, the device

checks whether the MFT1H register has a new message; if it

has, that message is sent once, otherwise the contents of

the MFT1L register are sent.

In TE modes on the receive side, the high priority messages

on the SC1 channel (LP, ST, FECV and DTSE) are accepted

as valid on the first occurrence and the MFR1 interrupt is

generated to indicate the status (see

Table 8).

Transmission of QH - High Priority Messages

In TE modes, a Loss of Power condition is conveyed to the

NT by writing the LP command in the MFT1H register for a

“one shot” high priority message which overrides any other

Q channel message. Write the LP message in the MFT1L

sages. Normal maintenance commands such as LB1 Re-

quest are written to the MFT1L register.

SC2 Channel Messages

With the MFC6E enabled, the TP3420A guarantees the 6x

transmission of SC2 messages according to the ANSI 1991

spec. The software should load an SC2 message in to the

MFT2 register within 30 ms of the MFC interrupt. The multi-

frame word for the SC2 stream is then transmitted on the

next 6x boundary and repeated 6 times. If the register is not

updated by another MFT2 message within 30 ms, then the

device will re-cycle the existing message in the SC2 register,

i.e. re-transmit it 6 times.

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