Description
The AT29C257 is a 5-volt-only in-system Flash programmable and erasable read only memory (PEROM). Its 256K of memory is organized as 32,768 words by 8 bits. Manufactured with Atmel’s advanced nonvolatile CMOS technology, the device offers access times to 70 ns with power dissipation of just 275 mW. When the device is deselected, the CMOS standby current is less than 300 µA. The device endurance is such that any sector can typically be written to in excess of 10,000 times.
To allow for simple in-system reprogrammability, the AT29C257 does not require high input voltages for programming. Five-volt-only commands determine the operation of the device. Reading data out of the device is similar to reading from a static RAM. Reprogramming the AT29C257 is performed on a page basis; 64-bytes of data are loaded into the device and then simultaneously programmed. The contents of the entire device may be erased by using a 6-byte software code (although erasure before programming is not needed).
During a reprogram cycle, the address locations and 64-bytes of data are internally latched, freeing the address and data bus for other operations. Following the initiation of a program cycle, the device will automatically erase the page and then program the latched data using an internal control timer. The end of a program cycle can be detected by DATA polling of I/O7. Once the end of a program cycle has been detected a new access for a read, program or chip erase can begin.

Features
• Fast Read Access Time - 70 ns
• 5-Volt-Only Reprogramming
• Page Program Operation
   Single Cycle Reprogram (Erase and Program)
   Internal Address and Data Latches for 64-Bytes
• Internal Program Control and Timer
• Hardware and Software Data Protection
• Fast Program Cycle Times
   Page (64-Byte) Program Time - 10 ms
   Chip Erase Time - 10 ms
• DATA Polling for End of Program Detection
• Low Power Dissipation
   50 mA Active Current
   300 µA CMOS Standby Current
• Typical Endurance > 10,000 Cycles
• Single 5V ± 10% Supply
• CMOS and TTL Compatible Inputs and Outputs
• Pin-Compatible with AT29C010A and AT29C512 for Easy System Upgrades