Motorola and V.32bis - Manual (Page 177)

Cabling and Interface Pinouts B-9
Inter
fa
ce
Pinouts
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
Table B-5.
Motorola DB-25 Low Capacitance Cables for 326X
Description
Motorola
Product
Code
Up to 19.2
kbps (ft) Up to 64.0
kpbs (ft) Up to 96.0
kbps (ft) Up to 115.2
kbps (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.