A safe and reliable IC card reader/writer system circuit

The picture shows the IC card and its reader/writer hardware circuit diagram. The reader/writer is composed of microcontroller, keyboard, display, monitoring circuit and other parts. The IC card uses X76F100Y of XICOR Company. 2.1 IC card and card holder X76F100 is a 128×8-bit confidential serial FLASH E2PROM, in which the read password and write password are 64 bits respectively. Figure 2 is the pin diagram of its Smart Card package. Encapsulate the chip on a card, insert the card into the card holder of the IC card reader, and the reader can read and write it to implement encryption, query, deposit, withdrawal and other functions. The IC card holder has 8 pins, and when the X76F100Y is inserted, it is connected to these pins. There are also two fixed ends, one of which is connected to a spring leaf on the card holder. The two contacts and the spring leaf are equivalent to a normally closed switch. When the card is not inserted, the reed is closed and P3.2 pin remains low; when the card is inserted, the reed is pushed open and P3.2 pin becomes high level. When the microcontroller detects that the P3.2 pin goes high, it makes the RST pin of the X76F100 go high through P1.3 to reset it. 2.2 Single-chip microcomputer The single-chip microcomputer adopts GMS97C52 of LG Company. It has 8K bytes of ROM, 256 bytes of RAM and 32 I/O ports. The P1 port is connected to the serial devices X25045 and X76F100. The P0 and P2 ports are used for keyboard and display. P3.2 in the P3 port is used for Detect whether the IC card is inserted, and the remaining 7 ports can be expanded with other functions. 2.3 Monitoring circuit The monitoring circuit uses the X25045 chip, which includes a watchdog timer, voltage monitoring circuit and E2PROM memory. Its function is: to generate a RESET signal to GMS97C52 when the power is turned on and off; the watchdog monitors the system to prevent it from crashing. 2.4 Keyboard circuit For convenience, the keyboard interface circuit is implemented with I/O port. It has a 4×4 structure and 16 keys. There are 11 numeric keys, 4 function keys, and 1 enter key. Numeric keys: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ← (backspace). Function key: Query? , Storage+, Withdrawal-, Change Password*. Inquire? : Users can check the amount deposited in the card by reading the password. Deposit+: Users can deposit money into the card by writing a password. Withdrawal -: Users can withdraw money from the card by writing the password. Change password*: divided into changing read password and writing password. For convenience, make the read password and write password consistent. Pressing this key will modify the read password and write password at the same time. Enter key: Confirm after entering the 8-digit password or the amount of deposits and withdrawals, and confirm after entering the new password. 2.5 Display circuit The display part adopts LED display and also uses I/O port. Used to display system status, entered password or amount to be deposited and withdrawn, as well as error messages, etc. Since the driving current of GMS97C52 is limited, inverter SN74F04 is added to the P0 and P2 ports to increase the driving capability. Its sink current is 64mA and its output current is 15mA, which can ensure the sink current required for bit selection.