mirror of
https://github.com/opsxcq/mirror-textfiles.com.git
synced 2025-08-22 10:13:37 +02:00
80 lines
3.4 KiB
Plaintext
80 lines
3.4 KiB
Plaintext
Title : PC to VideoCrypt and/or Smart Card interface via RS232 port.
|
||
|
||
The following interface has been built and used succesfully. It is loosely
|
||
based on Markus Kuhn's ADAPTER.TXT and can be used in three modes:
|
||
|
||
* PC listens to traffic between VideoCrypt decoder and Smart Card.
|
||
* PC pretends to be the Smart Card and talks to the VideoCrypt decoder.
|
||
* PC pretends to be a VideoCrypt decoder and talks to the Smart Card.
|
||
3 5 8
|
||
VCC oÄÂÄÄÄÄÄÄÂÄÄÂÄÄ¿
|
||
³ ÚÄÁÄÄÁÄÄÁÄ¿2
|
||
100 ÍØÍ 1Ä´ EXO-3C ÃÄÄo CLK output
|
||
nF ³ ÀÄÂÄÄÂÄÄÂÄÙ
|
||
GND oÄÁÄÄÄÄÄÄÁÄÄÁÄÄÙ
|
||
4 6 7
|
||
|
||
Qty Part Package Description
|
||
1x EXO-3C DIL 8 Programmable Oscillator 14.31818Mhz max frequency
|
||
|
||
CIRCUIT DESCRIPTION
|
||
|
||
The interface is designed to be connected to a PC with a 9 pin or 25 pin
|
||
RS232 port.
|
||
|
||
The PC's RS232 port operates with signals that swing from +12V to -12V. The
|
||
smart card however, operates with TTL signals that swing between +5V and 0V.
|
||
An RS232 -12V level corresponds to a TTL high (+5V) and a RS232 +12V level
|
||
corresponds to a TTL low (0V).
|
||
|
||
Due to this incompatibility, a signal level translator such as the MAX232
|
||
must be used. The MAX232 is powered from a single +5V supply and generates
|
||
internally the +/-12V voltages necessary for the RS232 communication.
|
||
The MAX232 needs external components to achieve this.
|
||
|
||
The DCD line is used to monitor the state of the RST line on the smart card.
|
||
This allows us to detect when a reset takes place.
|
||
|
||
The RXD line is used to receive data from the smart card.
|
||
|
||
All TTL signals from the MAX232 go to SC1 which is a smart card connector
|
||
accepting cards with contact locations that conform to the ISO7816-2 standard,
|
||
section 4, fig 2.
|
||
|
||
The final part of the circuit is a oscillator. This is only needed
|
||
if you intend to have the PC exchange data with a smart card. At all other
|
||
times the oscillator must be disconected. In the prototype the oscillator was
|
||
built on the board and a jumper is used to connect or diconect the oscillator
|
||
output to the card's CLK pin.
|
||
|
||
There are many options for building oscillators. Some people use discrete
|
||
components.
|
||
|
||
This Osc is a programmable frequency divider. This is a DIL 8 pin chip with
|
||
a built in crystal oscillator. The one in this project has a base frequency of
|
||
14.31818Mhz. Three pins on the chip allow a divisor between 2^1 to 2^8 to
|
||
be selected allowing frequencies between 7.15909Mhz and 55.93khz to be
|
||
produced. A separate output, provides the undivided base frequency. In this
|
||
project a divisor of 2^2=4 was selected effectively providing an output
|
||
frequency of 3.579545Mhz.
|
||
|
||
Oscillators are really noisy devices. They produce a lot of noise on the
|
||
power line. Therefore, a 0.1 uF capacitor _must_ be fitted as close to the
|
||
supply lines of the oscillator as possible. This not only eliminates the
|
||
noise on the supply lines but improves the sqareness of the generated
|
||
waveform.
|
||
|
||
Total current drawn at 5V with oscillator active is 7.6mA.
|
||
|
||
WARNING: Before attempting to connect the interface to any decoder, use a high
|
||
impedance DMM to measure the AC voltage difference between the interface GND
|
||
and the decoder's GND. If the difference is not close to 0VAC, earth the
|
||
decoder's GND before connecting the interface. Use at your own risk. If you
|
||
damage something you have no one to blame but yourself for stuffing with it
|
||
in the first place. Take care.
|
||
|
||
Regards
|
||
|
||
paul
|
||
|