Lee ,
firstly your 0.02 $ ...your advice is more expensive then this ...:)
iam thankful for your and Dennis Welbourn suggestions.
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i have got the datasheets and iam reading it day in and day out. I swear that i really work hard , people on this forum think that i only play around... i have basic electronics knowledge but still a project like "design a 2+8 PBX " is a tough ask for any one.

so i have decided to first copy a existing system and then moves on to design mine as it happens in our college ages where we do a example numerical and after that go for the real exercise question..

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here is the detail i have gathered using datasheet and that circuit ...

iam looking forward to understand how the scanning of SLIC lines is done.

At89c52 Pin outs in this PBX which is only for 16 extension Lines No trunk involved:-

89c52 MT8816

P1.0 pin 24 (Ay0) address line input
P1.1 pin 25 (Ay1) address line input
P1.2 pin 2 (Ay2) address line input
P1.3 pin 5 (Ax0) address line input
P1.4 pin 22 (Ax1) address line input
P1.5 pin 23 (Ax2) address line input
P1.6 pin 4 (Ax3) address line input
P1.7 pin 38 DATA PIN

(DATA PIN: a logic high will turn on a selected switch & a logic low will turn off the selected switch, active high)

Pin9 Pin 3 ( to REST circuitary)

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then :-

Pin10 is not used in the circuit (RXD)

Pin11 (TXD) connected to Pin no. 4 of SN751768P (Pin No.4 = D)

(SN751768P :- differential Bus Transceiver)

Pin 12, Pin 13, Pin 14 not used.

Pin 15 ---- MT8816 Strobe Pin.

( what is a strobe ?)

Crystal of 11.05Koh is used

Two HCF4094BE (8 stage shift & store bus regsiter with 3-state outputs) are used in the circuit
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Controller Pins HCF4094BE Pins

Pin 2.0 DATA input (Pin No.2)

Pin 2.1 CLOCK input (Pin No.3)
and the same connection goes to the second 2nd HCF4094BE CLock pin.



Two MC74HC165N (8 bit parallel in and serial out shift register) are used in the circuit
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Controller Pins 74HC165 Pins

Pin 2.3 Clock input (Pin No.2) (low to high trigged, CP) and the same connection goes to the second 2nd 74HC165 CLock pin.

Pin 25 goes to :-

Pin No.9 ( Q7 serial output from the last stage) of 74HC165.

From the Gnd Pin of 74HC165 the above shift resgister connection goes to Pin No.9 i.e. Q7 of second 74HC165.

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Controller Pin No. 26 and 27 not used, Pin 28 and from 32 to 39 not used.


Now can some one make out of something from the above description....