AN1500A South African Micro-Electronic Systems, AN1500A Datasheet - Page 9

• Manufacturer Part Number: AN1500A
• Description: Single Chip Telephone Demo Board
• Manufacturer: South African Micro-Electronic Systems

10 Sliding cursor protocol and pause insertion
To accommodate easy and uncomplicated redialing behind a PABX, a sliding cursor protocol is implemented:
if a manually entered digit string matches the contents of the LNR memory, pressing LNR will only dial out the
remaining digits :
example: desired number 0123456 (where 01 is the access code)
11 AC impedance of the SA2532K
The SA2532K is designed for applications requiring a characteristic impedance of 600 Ohms, no connection should
be made to CI (pin 7) if a real impedance is required. Should a complex impedance be required a capacitor of
approximately 1/10 of the complex part of the impedance should be connected to CI. Every complex impedance
consists of a real and complex part. The ac impedance of the SA2532K is calculated by
Where :
Z1 = the external resistor connected between pin 1(LS) and pin 27 (LI) . This resistor is also used by the device for
current monitoring and sets the DC resistance. To maintain correct operation the value of this resistor should be
set to 30 Ohm.
Z
For real impedances
If a impedance lower than Z
V
considered. For example, if a bipolar line transistor is used, the resistance from the transistors base to VSS (Z
in the order of 10K (R10). If a MOSFET is used then Z
Care must be taken when selecting the value of ZP since the value chosen should be such that the line transistor is
driven into full saturation.
11.1 Demo board measurements:
11.1.1 Definition:
return loss is defined as:
9/27
SYN
SS
. To calculate the resulting AC impedance, any parallel impedance path between LS and V
AN1500A
= the internally synthezised impedance.
off-hook, manual entry = 01
off-hook, manual entry = 01
where:
Z
Z
Zref = the reference AC impedance (= the line termination)
Zx = the AC impedance of the telephone under test
AC
AC
= Z
= 600//Z
AC
SYN
is required, then a external parallel impedance should be added between LS and
Z
+ Z1
returnloss
Z
SYN
Z
P
AC
AC
sames
sames
sames
sames
= 19 * Z1
= (19*Z
= 20 * Z1 = 600 Ohm
-wait for dial tone
(LNR contents is 0123456)
-wait for dial tone
LNR dials out the remaining digits: 23456
SYN
20 * log
) + Z1
Zref
Zref
P
is in the order of 100K which is negligible.
-23456
- press LNR key:
Zx
Zx
- line is busy
-on-hook
SS
should be
P
) is