Motorola 326X V.34, and V.32bis, V.34-SDC manual Table B-4 Maximum Cable Capacitance per Data Rate

Interface Pinouts

Table B-4shows a range of data rates and maximum allowable capacitances. The maximum capacitance is a total of the inter-conductor capacitance (between the conductors represented as Cc in Table B-4), and the capacitance between the shield and the conductor (represented as Cs in Table B-4).

Table B-4.

Maximum Cable Capacitance per Data Rate

Data Rate	Maximum Cable Capacitance (Cc+Cs) in
(kbps)	Pico Farads (pF)*
0-20.0	2400 pF
20.0-64.0	900 pF
64.0-96.0	400 pF
115.2	200 pF
Notes:

*(1) The total capacitance in this column is the total allowable cable capacitance.

(2) Maximum resistance of cable conductors is 25 Ohms.

The maximum allowable cable capacitance decreases as DTE rates increase. The more capacitance in the cable, the shorter the allowable length at a DTE rate. Similarly, the allowable lengths become shorter as DTE rates increase.

Since newer PCs support EIA 232-D type receivers/drivers at higher rates, you must use information in this section to determine cable length.

To determine the per foot capacitance of your cable:

1)Determine the length of the cable you require for your application.

2)Determine the range of rates that the modem will use. (For example, to routinely operate the modem’s DTE port between 20.0 and 96.0 kbps, determine the cable capacitance for the higher rate. You can operate the modem up to, but not exceeding, the maximum rate capacitance that you calculate.)

3)Refer to Table B-4for the maximum allowable cable capacitance for a given rate. (For example, to operate the modem at 64.0 kbps, the maximum capacitance is 900 pF.)

4)Divide the maximum cable capacitance by the length of the cable. This results in the total cable capacitance per foot. The formula below illustrates how to calculate the per-foot capacitance:

Maximum Cable Capacitance (pF)		Maximum Cable Capacitance (pF)
	=
Total Cable Length in Feet		per Foot

B-8 Cabling and Interface Pinouts