FC106

Revision 1.2

14/32

September 98

3.13 I/O impedance control

The ZC block sets the internal RX+/RX- and the TX+/TX- matching impedance. Table 3.1

details the different settings.

Table 3.1

ZC block settings

Case 3 and 4 are identical applications: Case 3 allows better on board compatibility with other

FC parts that request 25

Ω series resistors. Exact value of R

5.3:

DC characteristics on page 18.

ZC+

ZC-

ADD Rs

+/-1%

ADD Rc

+/-1%

Case 1: 50

Ω line

LINE = 50

Ω

External Rc

OPEN

OPEN

0

Ω

100

Ω

Case 2: 50

Ω line

LINE = 50

Ω

No external Rc

Use internal Rc

OPEN

0

Ω

NONE

Case 3: 75

Ω line

LINE = 75

Ω

External Rc

OPEN

OPEN

25

Ω

150

Ω

Case 4: 75

Ω line

LINE = 75

Ω

External Rc

OPEN

0

Ω

150

Ω

Case 5: 75

Ω line

LINE = 75

Ω

No external Rc

Use internal Rc

0

Ω

NONE

receiver

transmitter

Rs = 0

Ω

Rs = 0

Ω

receiver

transmitter

Rs = 0

Ω

Rs = 0

Ω

receiver

transmitter-

Rs = 25

Ω

Rs = 25

Ω

receiver

transmitter

Rs = 0

Ω

Rs = 0

Ω

receiver

transmitter

Rs = 0

Ω

Rs = 0

Ω