1-Fiber Modem

60

59

58

57

56

55

54

53

52

51

50

49

48

47

46

45

44

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

1

CKC

2

SETB

3

GND

4

XI1

5

TxD3

6

XI2

7

TxD4

8

HBT

9

DCD

10 GND

11 CLK9

12 RxD2

13 RxD1

14 XTI

15 XTO

16 GND

17 GND

18 NC

19 VD+

20 VD+

21 TxCL

22 TxD2

23 ERRL

24 TxD1

25 RxCL

26 NC

27 IC

28 DCDB

29 VD+

30 ERRC

31 RxD4

32 XO2

33 XO1

34 RxD3

DM3

68

VD+

67

DM2

66

DM1

65

DR1

64

DP2

63

DP1

62

NC

61

NC

60

NC

59

TRC

58

IC

57

VA+

56

LAP

55

LAN

54

PINP

53

PINN

52

CON2 51

CNT

50

AGND 49

CON1 48

VG+

47

NC

46

NC

45

NC

44

GND

43

DP3

42

GND

41

PORB 40

DP4

39

DR4

38

DR3

37

GND

36

DR2

35

Figure 1. Top view of 68 PLCC package

NC = Not Connected IC = Internally Connected

ERC produces a pulse on detection of each coding error. These

pulses may be accumulated by means of an external electronic

counter.

Please note that ERL and ERC detect coding errors and not data

errors, nevertheless because of the complexity of the coding rules

on the ACS401 the absence of detected errors on these pins will

give a good indication of a high quality link.

LASER/LED Considerations

Since LEDs or LASERs from different suppliers may emit different

wavelengths, it is recommended that the LASERs/LEDs in a

communicating pair of modems are obtained from the same

supplier. Furthermore, the emission spectrum is a function of

temperature, so a temperature difference between the ends of a

link reduces the responsivity of the receiving LASER/LED,

resulting in a reduction in the link budget. Information is given in

the suppliers’ data sheets. The following manufacturers have

components that will be tested with the ACS401 and Acapella will

be glad to assist with contact names and addresses on request:

LED Suppliers

ABB-Hafo (e.g.1A-212ST, 1A-212SMA)

Acapella

(e.g.A-ST, A-SMA)

GCA

(e.g.1A-212-ST-05, 1A-212-SM-02)

Honeywell (e.g.HFE4214-013, HFE4404-013)

Duplex Suppliers

GCA

90-0359

Siemens

SBM 51214X

Operating Wavelengths

The ACS401 can support any wavelength LED, ELED or LASER,

from 660 nm through to 1500 nm.

Power Supply Decoupling

The ACS401 contains a highly sensitive amplifier, capable of

responding to extremely low current levels. To exploit this

sensitivity it is important to reduce external noise to a low level

compared to the input signal from the LASER/LED. The modem

should have an independent power trace to the point where power

enters the board.

Figure 3. shows the recommended power supply decoupling. The

LASER/LED should be sited very close to the PINN, LAN and LAP

pins. A generous ground plane should be provided, especially

around the sensitive PINN, LAN and LAP pins. The modem

should be protected from EMI/RFI sources in the standard ways.

Link Budgets

The link budget is the difference between the power coupled to the

fiber via the transmit LASER/LED and the power required to

realise the minimum input amplifier current via the receive

LASER/LED/PIN. The link budget is normally specified in dB or

dBm, and represents the maximum attenuation allowed between

communicating LASER/LEDs. The budget is utilised in terms of

the cable length, cable connectors and splices. It usually includes

an operating margin to allow for degradation in LASER/LED

performance. The power coupled to the cable, is a function of the

efficiency of the LASER/LED, the current applied to the

LASER/LED and the type of the fiber optic cable employed.

The conversion current produced by the reverse biased

LASER/LED or PIN is a function of the LASER/LED/PIN efficiency

and the fiber type. The conversion efficiency is measured in terms

of its ability to convert the available optical power to current,

known as the responsivity, given in (A/W). Some examples of link

budgets are given in the tables headed, Link Budget Examples.

Digital Mode

The ACS401 may be used as a controller and data buffer which

allows the device to be used with an external amplifier for non-

fiber applications. Check with Acapella for details.

Data delay and skew

The Full Duplex Delay (FDD) of TxD and control signals XI(1:2)

when using the recommended XTAL frequency of 9.216 MHz

=

4 ms (‘standard’mode)

=

8 ms (‘double’ mode)

XI FDD

9.216MHz

=

10 ms (‘standard’mode)

XI FDD

9.216MHz

=

20 ms (‘double’ mode)

For other XTAL frequencies, the delay is inversely proportional to

the XTAL frequency using the above delays as the constant of

proportionality.

9.216MHz

The synchronous data skew between the main data channels

RxD1, RxD2, RxD3 and RxD4 across the link is zero data-bits.

ACAPELLA

ACS401