In SX Microcontrollers, SX/B Compiler and SX-Key Tool, william wrote:

Sometime ago we said we wanted to develop a keyphone system based on the SX.

Here it is in ExpressPCB format. ( See attachments )

The board is now sitting on my desk.  It is truly as sight to behold !
2 lines, 4 extensions only, yet more than a hundred resistors.  :shocked: 

Any comments and ideas?
Anybody wants to help us develop the firmware for this monster?
It has to be in assembly language. ( I don't know SX/B )

How its supposed to work:-
The SX52 will sample voice from one port ( line or ext ) using software ADC and then play it on the other port on the fly using PWM.

This reference design covers

1.  DTMF Detection and Generation
2.  Ring Detection for lines
3.  Hook and Flash Detection for Exts
4.  Ring Voltage Generation
5.  Power Failure bypass to Ext1 and Ext2
6.  Hybrid circuits to reduce echo
7.  Serial Connection to PC for Call Detail Dump

CallerID snoop not included cos we have run out of pins.

Have fun.

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