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Exar Coporation 48720 Kato Road, Fremont CA, 94538 • (50) 668-7000 • Fax (50) 668-707 • www.exar.com

SP505_00_08308

LOOPBACK MODE...

The SP505 is equipped with two loopback

modes. Single-ended loopback internally

connects V.28 driver outputs to V.28 receiver

inputs. The signal path is non-inverting and

will support data rates up to 20kbps. The

propagation delay times are as specified

in the electrical specifications. To initiate

a single-ended loopback, the code "00"

should be written to the driver decoder.

Differential loopback is implemented by

applying "0" to the driver decoder. This

internally connects V. driver outputs to

V. receiver inputs. The signal path again

is non-inverting; the differential loopback

data rate can be at least 5Mbps.

Under loopback conditions the receiver

decoder is disabled. While the SP505 is in

either single-ended or differential loopback

mode, the driver outputs are tri-stated and

the receiver inputs are disabled.

Mode

Driver Output

Receiver Input

Driver Receiver

non-inverting

inverting

non-inverting

inverting

Input

Output

Loopback

DEC = 1010

tri-state

tri-state

>10KΩ to GND >10KΩ to GND active

active

DEC = 1011

tri-state

tri-state

>10KΩ to GND >10KΩ to GND active

active

Power down

clamped

V

tri-state

tri-state

>10KΩ to GND >10KΩ to GND inactive at ±0.6V

Tri-state

DEC = 0000

tri-state

tri-state

>10KΩ to GND >10KΩ to GND inactive tri-state

DRIVER/RECEIVER

DEC

DEC

0

RD(a) 70

RxD 1

RT(a) 37

RxC 20

SCT(a) 76

SCT 79

SCTEN 7

SCT(b) 77

15 TxC

63 TT(a)

65 TT(b)

6

TTEN

RECEIVERS

DRIVERS

22 ST

42 ST(a)

44 ST(b)

23 STEN

CS(a) 66

CTS 80

RR(a) 35

DCD 19

RR(b) 36

CS(b) 67

RT(b) 38

RD(b) 71

1

0

1

1

24 LL

51 LL(a)

49 LL(b)

5

LLEN

14 TxD

61 SD(a)

59 SD(b)

2 SDEN

13 DTR

58 TR(a)

56 TR(b)

3 TREN

16 RTS

54 RS(a)

52 RS(b)

4 RSEN

17 RL

47 RL(a)

45 RL(b)

18 RLEN

IC(a) 39

RI 21

IC(b) 40

DM(a) 68

DSR 78

DM(b) 69

IC(a) 39

RI 21

SCTEN 7

RECEIVERS

DRIVERS

1

0

1

0

24 LL

51 LL(a)

5 LLEN

13 DTR

58 TR(a)

3 TREN

DM(a) 68

DSR 78

16 RTS

54 RS(a)

4 RSEN

17 RL

47 RL(a)

18 RLEN

RR(a) 35

DCD 19

CS(a) 66

CTS 80

RD(a) 70

RxD 1

RT(a) 37

RxC 20

SCT(a) 76

SCT 79

14 TxD

61 SD(a)

2 SDEN

15 TxC

63 TT(a)

6 TTEN

22 ST

42 ST(a)

23 STEN

DRIVER/RECEIVER

DEC

3

DEC

DEC

0