IBM 1 Series - Page 115

4-10 GA34-0033
Generally, most users will elect to use either the EIA-voltage-level
interface or the nonisolated current loop interface.
If a user is in doubt as to which interface to select, the EI[A-voltage-level
interface should be used.
If the user’s environment is electrically noisy, the nonisolated current loop
interface should be used.
The following table outlines the advantages and disadvantages of each of
the four interfaces incorporated into the teletypewriter adapter card:
Interface
EIA voltage level
Nonisolated current loop
Isolated current loop
TTL voltage level
Advantages
Customer does not have to
purchase OEM power supplies
to drive current loops
Simple cabling from card to
device
Most OEM devices support
EIA interface
Simple cabling from card to
device
High noise immunity
Customer does not have to
purchase OEM power supply
to drive current loops
High noise immunity
+12-volt power feature not
required
+12-volt power feature not
required
Simple cabling from card to
device
Disadvantages
+12-volt power feature is a
prerequisite for this
interface
+12-volt power feature is a
prerequisite for this
interface
OEM devices may not have
a current loop position
Customer must purchase
two OEM power supplies to
drive current loops
Customer must furnish
cabling from the
teletypewriter adapter to
power supplies to attached
device
OEM devices may not have
a current loop position
Few OEM devices offer this
interface