ACE9050 datasheet(37/52 Pages) MITEL

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ACE9050

VC_CCN

Mode

ENWS

Description

Data reframe = disabled

IRQ-BI-SAT = Busy/Idle

Busy/Idle bits extracted

Data reframe = enabled

IRQ-BI-SAT = Not Valid

Busy/Idle bits not extracted

Data reframe = disabled

IRQ-BI-SAT = SAT update

Data reframe = enabled

IRQ-BI-SAT = SAT update

Control channel syncronised

Control channel unsynchronised

Voice channel

Table 78

Control Channel

When on a Control channel the software must decide when

to switch between the synchronised and unsynchronised modes.

The Modem does not give any direct indication that bit

synchronisation has been achieved; however, the IRQ-WS

provides indication that a Barker code has been detected. The

system designer can look for the IRQ-WS being generated

regularly in a suitable time window corresponding to the frame

time, RSSI levels and squelch levels, before determining the

Modem is in synchronisation.

Once the software has determined that the Modem is in

synchronisation the ENWS bit must to be set to zero. The Word

Sync Detector will then remove the Busy/Idle bits from the

incoming data stream and not re-synchronise on Barker codes.

The software must disable ENWS before the first Busy/Idle bit

occurs after the Barker Code in the control channel frame. The

time for this is 1ms on AMPS or 1·25ms on TACS systems. The

software does not then have to re-enable ENWS unless

synchronisation is lost.

As the number of bits in a frame is not divisible by eight the

Word Sync Detector circuit uses frame counters to realign the

data on subsequent frames instead of Barker codes. This

ensures spurious Barker codes occurring in the data do not upset

the synchronisation of the Modem. Due to this action Barker

codes will appear distorted when read in the RXD registers. The

dotting and Barker code will appear as the following three

consecutive bytes: AAH, B8H and 12H. Once in synchronisation,

the software must ensure that the IRQ-WS still occur within the

time window set up. If a number of IRQ-WS are missed, the

software must assume the Modem has become unsynchronised

and take appropriate action. It is up to the system designer to

decide on the threshold for the number of IRQ-WS dropped, or

any other type of software averaging . Table 79 shows a typical

sequence for locking onto data when on a Control channel.

Voice Channel

Data is not a continuous stream on a Voice channel, as on a

Control channel. The data sequence also does not contain Busy/

Idle bits. The software designer has to determine when valid data

is present on the voice channel. The IRQ-WS interrupt timinq

cannot be used for this purpose, as the data stream is not

continuous. Also IRQ-WS interrupts will occur sporadically, even

when no data is present, due to the probability of an incoming

signal beinq decoded as a valid Barker code.

The voice channel data sequence begins with a long dottinq

sequence. The software can monitor the data present in the RXD

registers, and when these reliably yield a pattern of AAH or 55H

it can be assumed a data sequence is beinq transmitted. The

software should then ensure an IRQ-WS occurs to indicate valid

data is beinq received. Other system parameters such as RSSI,

RX audio level and SAT can also be measured by the software.

ENWS may be left enabled, or disabled after synchronisation.

As there are no Busy/Idle bits and the frame is divisible by eight

it is not critical to the hardware operation.

Data Transmitter

The Modem transmitter is considerably simpler than the

receiver. It contains a data register for writing data 8 bits at a time

and Manchester encoding circuitry. It also contains timing and

interrupt circuitry.

Data to be transmitted is written one byte at a time to

TXD[7:0]. This data is then transmitted on the next IRQ-TX

interrupt, if the output is enabled. Bit 7 (most significant) is

transmitted first. The Data Transmitter generates the IRQ-TX

interrupts at the correct rate for the chosen system (800

µs for

AMPS or 1000

µsforTACS)regardlessofwhetherthetransmitter

is enabled or not. The Transmitter encodes the data into

Manchester format before transmission. This is achieved by

Description

Function

ENMOD = 1

MDMSLP = 0

MDMRESN = 1

LF1_2 = 0

RXDINV = Setup to system

NOMPLL = 0

SQLEV[3:0] = Set as required

A_TN = Set as Required

Disable all Modem Interrupts

VC_CCN = 0

SYNDET = 0

ENWS = 1

Enable IRQ-WS interrupt

Ensure the IRQ-WS

interrupts are occurring in

the correct time window.

It is up to the system

designer to determine

the exact criteria.

When this occurs set:

ENWS = 0 within 1ms

SYNDET = 1

Enable IRQ-RX interrupt

within 800

µs.

Read and Squelch on interrupt

Ensure IRQ-WS occurs

in correct time window.

The data registers should

contain AAH, B8H & 12H

at the end of a frame.

Set up

Initialise

Acquire

Verify

Lock

Read Data

Check

Table 79 Data sychronisation and acquisition sequence

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