Pin Name
I/O
Internal
Connection
Description
MODE
I/O
CMOS
IN/OUT
This is a three-state input/output pin, used for dialing mode
selection, either Tone mode or Pulse mode, 10pps/20pps
MODE=VDD: Pulse mode, 10pps
MODE=OPEN: Pulse mode, 20pps
MODE=VSS: Tone mode
During the pulse mode dialing, switching this pin to the tone
mode changes the subsequent digit entry to the tone mode.
When the chips are in tone mode, switching to the pulse mode
will also be recognized.
DTMF
O
CMOS OUT
This pin is active only when the chip transmits tone dialing
signals. Otherwise, it always outputs a low. The pin outputs
tone signals to drive the external transmitter amplifier cir-
cuit. The load resistor should not be less than 5k .
HDI
I
CMOS IN
Pull-high
This pin is a schmitt trigger input structure. Active low. Ap-
plyinganegativegoingpulsetothispincantoggletheHDOout-
put once.
An external RC network is recommended for input
debouncing. The pull-high resistance is 200k
typ.
HDO
O
CMOS OUT
The HDO is a CMOS output structure. Its output is toggle- con-
trolled by a negative transition on HDI. When HDO is toggled
high,POkeepshightoholdtheline.Theholdfunctioncanbere-
leased by setting HFO high or by an on-off hook operation or by
another HDI input. The HDO pin can directly drive the HT3810
seriesmelody generator to produce a hold-line background mel-
ody. Refer to the functional description for the hold-line func-
tion.
HFI
I
CMOS IN
Pull-low
This pin is a schmitt trigger input structure. Active high. Ap-
plying a positive going pulse to HFI can toggle the HFO once
and hence control the hand-free function.
An external RC network is recommended for input
debouncing. The pull-low resistance of HFI is 200k
typ.
HFO
O
CMOS OUT
The HFO is a CMOS output structure. Its output is toggle-
controlled by a positive transition on the HFI pin. When HFO
is high, the hand-free function is enabled and PO outputs a
high to connect the line.
The hand-free function can be released by an on-off-hook oper-
ation or by another HFI input or by setting HDO high. Refer to
the functional description for the hand-free function opera-
tion.
DOUT
O
NMOS OUT
NMOS open drain output pin. It outputs the BCD code of the
dialing digits to the LCD driver chip (HT16XX series) or C for
dialing number display. Refer to the functional description for
the detailed timing.
HT9320
6
July 21, 1999