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NS7520 Features
4
NS7520 Hardware Reference, Rev. D 03/2006
Programmable timers
– Two independent timers (2μs–20.7 hours)
– Watchdog timer (interrupt or reset on expiration)
– Programmable bus monitor or timer
Operating frequency
– 36, 46, or 55 MHz internal clock operation from 18.432 MHz quartz crystal
or crystal oscillator
– f
MAX
= 36, 46, or 55 MHz (grade-dependent)
– System clock source by external quartz crystal or crystal oscillator, or clock
signal
– Programmable PLL, which allows a range of operating frequencies from 10
to f
MAX
– Maximum operating frequency from external clock or using PLL
multiplication f
MAX
Bus interface
– Five independent programmable chip selects with 256 Mb addressing per
chip select
– All chip selects support SRAM, FP/EDO DRAM, SDRAM, flash, and EEPROM
without external glue
– Supports 8-, 16-, and 32-bit peripherals
– External address decoding and cycle termination
– Dynamic bus sizing
– Internal DRAM/SDRAM controller with address multiplexer and
programmable refresh frequency
– Internal refresh controller (CAS before RAS)
– Burst-mode support
– 0–63 wait states per chip select
– Address pins that configure chip operating modes; see "NS7520 bootstrap
initialization" on page 60.