SAN3010

sames

sames

sames

sames

6/13

Flowchart for Microcontroller interface to AS253x single-chip-telephone

Notes: RowX,ColX,ColY: see table1

1 tclk= 256/3.58MHz = 71.5µs

all timings: Tol.:+-30µs

wait >20ms after AS253x

off-hook to ensure correct

start-up

Start

Loop=0

Row1 force low

all other rows/cols=Hi Z

Col Y=high ?

No

sync

Yes

delay4

wait 4.5 tclk=321µs

and disable all rows/cols=

Hi Z

delay3

wait 4.5 tclk=321µs

and force RowY low

all other rows/cols= Hi Z

=SCAN2

delay2

wait 1.5 tclk=107.25µs

and disable all rows/cols=

Hi Z

delay1

wait 1 tclk=71.5µs

and force RowX high

all other rows/cols= Hi Z

=SCAN1

delay5

wait 4.5 tclk= 321µs

and force ColX high

all other rows/cols= Hi Z

=SCAN3

Loop = 9 ?

Loop= Loop+1

No

delay6

wait 1.5 tclk=107.25µs

and disable all rows/cols=

Hi Z

delay7

wait 24*9 tclk=15.5ms

Yes

another key entry?

Yes

No

end

Key_in

12 Appendix B: Flowchart: