Heathkit H9 Manual page 18

Page 16
TTY (Passive) Connections
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PICTORIAL 2.'],O
TTY (20 mA current loop) Serial Input/Output
Passive
In the passive configuration, the 20 mA loop current
is supplied by the external device. pictorial Z_tO
shows the jumper wires necessary for the TTy (pas_
sive) configuration on the I/O circuit board. A maik is
defined as 20 mA flowing in the current loop. A space
is defined as less than 4 mA flowing in the current
loop. Pictorial2-1.1, shows the partial schematic of the
TTY (passive) wiring. The jumper wire that disables
the reader control is shown in pictorials 2-10 and
2-11. Refer to "Reader Control" on page 1g.