Motorola and V.32bis 用户手册

Cabling and Interface Pinouts B-9

For example, assume you require a 30-foot cable. You intend to operate your 
modem at 64.0 kbps. After looking at Table B-4, you determine that the 
maximum capacitance for the cable is 900 pF. According to the formula above, 
divide 900 pF by 30 feet. The result is 30 pF per foot:

Motorola recommends you use Motorola cables to attach your 326X modem(s) to 
DTE(s). Use Table B-5 to select cable(s) for your application.

To use non-Motorola cables, Table B-6 provides examples of vendor cable wire 
length versus DTE rates for 326X stand-alone units. NOTE: The part numbers 
specified in Table B-6 are not for complete cables, but for the wires that are available 
with the correct capacitance to support the higher rates of the 326X Modem.

900 pF

30 ft

= 30 pF/ft

Motorola 
Male 25-Male 25
Straight-through

92153

92152

92151

92150

50

30

10

6

Motorola 
Male 25-Female 25
Straight-Through

92157

92156

92155

92154

50

30

10

6

Motorola 
Male 25-Female 25
Crossover

92161

92160

92159

92158

50

30

10

6

NOTE: Motorola DB-25 Cables have a conductor capacitance of 11 pF/ft and a shield 
capacitance of 20 pF/ft for a total capacitance of 31 pF/ft. For example, operating at 19.2 
kbps, a 50-ft length of cable multiplied by a total capacitance of 31 pF/ft yields a maximum 
allowable cable capacitance of 1550 pF, which is acceptable in accordance with Table B-4.