How to connect multiple AT28C256/AT93C256/AT24C256/24LC512 EEPROMS to have more space
The AT28 and AT93 are 2 quite different families of parts.

The AT93 uses a serial interface known as SPI, and usually comes in an 8 pin package. It is very easy to interface to using almost any microcontroller, and is adequate for most purposes. This part, and the similar 24LC part that uses I2C are very common parts.

The AT28 uses an 8-bit parallel interface, and comes in a 28-pin package. It is relatively difficult to interface to using a microcontroller, and is normally only used in microprocessor designs which use a full databus. However it is capable of higher read and write speeds. It is not a very common part.

Assuming that you want 1M byte of EEPROM then the AT93C56 is definitely not the part to use. It has just 256 bytes of memory, you will need 4000 chips to give you 1 MB. You need to use a AT25M02 which has 2M bit of memory, so 4 chips will give you 1M byte. These are connected as follows:







simulate this circuit &ndash; Schematic created using CircuitLab