W91550DN SERIES
Publication Release Date: November 1997
- 5 -
Revision A3
Pin Description, continued
SYMBOL
PIN
I/O
FUNCTION
HFI
, HFO
57, 58
I, O Handfree control pins. A low pulse on the
HFI
input pin toggles the
handfree control state.
Status of the handfree control is listed in the following table:
CURRENT STATE
Input
HFO
Dialing
High
Yes
On Hook
High
Low
No
Off Hook
High
Low
Yes
On Hook
Off Hook
Low
Yes
Off Hook
Low
On Hook
Low
No
Off Hook
High
On Hook
High
Yes
Low
Hook SW.
HFO
HFI
NEXT STATE
HFI
HFI
−
−
HFI
pin is pulled to V
DD
by internal resistor.
Detailed timing diagram is shown in Figure 4.
LOCK
64
I
The
LOCK
pin is used to prevent "0" or "9" dialing under PABX
system long distance call control. When the first key input after reset
is "0" or "9", all the key inputs, including "0" or "9" key, become
invalid, and the chip generates no output.
The telephone is reinitialized by a reset.
The following table describes the functions of the
LOCK
pin:
LOCK PIN
Floating
V
DD
SS
V
FUNCTION
Normal dialing
"0", "9" dialing inhibited
"0" dialing inhibited
TEST
37
I
In normal operation, pulling the
TEST
pin to V
DD
inhibits the single
tone. In testing operation, pulling the
TEST
pin to V
SS
enables a
single tone to be created by pressing two keys simultaneously, and all
of the timing parameters for pulse dialing are faster than in normal
operation.
V
LCD
59
I
Power supply pin for LCD driver.
A 1
µ
F capacitor is connected between V
LCD
and V
SS
.
CP, CN
60, 61
I
CP is the voltage control capacitor positive pin.
CN is the voltage control capacitor negative pin.
A 1
µ
F capacitor is connected between these two pins.
