STATUS[1]

Field

Pos.

Meaning

STA_H

0

Transmit synchronisation in progress. Valid only in modem mode.

STA_CCITT

2

CCITT 2100Hz versus 2225Hz answer tone detect. Valid if STA_AT is set. Valid only in

tones modes.

STA_AT

3

Answer tone (either 2100Hz or 2225Hz) detected. Valid only in tones modes.

STA_HR

4

Receive synchronisation in progress. Valid only in modem mode.

STA_FLAG

6

V.21 channel 2 flag detect. Valid only in FAX modem mode and tone mode.

STA_DTMF

7

DTMF digit detect. The digit itself is available in the optional status byte STAOP2. Valid

only in DTMF receive mode.

VII.2.4 - Quality Status

The quality byte STAQUA monitors an evaluation of the line quality. It is updated once per baud and its

value ranges from 127 (perfect quality) to 0 (terrible quality). This value is automaticaly adjusted according

to the current receiving mode. Refer to the following chart to convert the value into its Bit Error Rate

equivalence.

1e

-3

1e

-4

1e

-5

1e

-6

1e

-7

1e

-8

1e

-9

0

31

63

95

127

STAQUA

BER

1e

-2

VII.2.5 - Optional Status

According to the operating mode of the ST75C520 the optional status is displaying different informations.

The optional status are automatically reprogrammed after each CONF command with the address of the

variables to monitor according with the operating mode selected (CONF_OPER). After the CONF command

the user must overwrite this default programming by using the DOSR command.

VII.2.6 - Default Optional Status in Tone Mode

While in tone mode the format of the STAOP word is as follows :

Add.

Name

Bit

765

4

321

0

$0C

STAOP0

TDT7

TDT6

TDT5

TDT4

TDT3

TDT2

TDT1

TDT0

$0D

STAOP1

TDT15

TDT14

TDT13

TDT12

TDT11

TDT10

TDT9

TDT8

$0E

STAOP2

RING_PERIOD

(1)

Notes : 1. RING_PERIOD is valid when the bit 3 of the STATUS[0] (STA_RING) goes high. This value is updated at each falling edge of

the RING signal. The RING_PERIOD value must be divided by 2400 to obtain the period in seconds.

2. TDTx is the output of the tone detector x.

ST75C520

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