W91820N SERIES
Pin Description, continued
SYMBOL 20-PIN 22-PIN I/O
FUNCTION
HFI, HFO
-
11, 12 I, O Handfree control pins.
A low pulse on the HFI input pin toggles the handfree
control state. The status of the handfree control state is
listed in the following table:
CURRENT STATE
NEXT STATE
HOOK SW. HFO INPUT HFO DIALING
-
On Hook
Low HFI
High HFI
High Yes
Low
No
Off Hook High HFI
Low Yes
On Hook
- Off Hook Low Yes
Off Hook Low On Hook Low
No
Off Hook High On Hook High Yes
The HFI pin is pulled to VDD by an internal resistor.
A detailed timing diagram is shown in Figure 3.
BLOCK DIAGRAM
HKS
HFI
XT XT
SYSTEM CLOCK
GENERATOR
ROW
(R1 ~ R4, Vx/R5)
COLUMN
(C1 ~ C4, Vss)
KEYBOARD
INTERFACE
DTMF
D/A
CONVERTER
READ/WRITE
COUNTER
CONTROL
LOGIC
LOCK
MODE
LOCATION
LATCH
RAM
PULSE
CONTROL
LOGIC
ROW & COLUMN
PROGRAMMABLE
COUNTER
DATA LATCH
& DECODER
T/P MUTE
KT
DP
HFO
H/P MUTE
Publication Release Date: May 1999
-5-
Revision A2