AR# 499: XC4000/XC5200 - What is the tolerance of the internal clock of XC4000/XC5200 devices?
AR# 499
XC4000/XC5200 - What is the tolerance of the internal clock of XC4000/XC5200 devices?
描述
General Description:
What is the tolerance of the internal clock of XC4000/XC5200 devices?
解决方案
The Data Book indicates that the frequency spread of XC4000/XC5200 internal clock = +25% to -50%. Given that the nominal frequency is 8 MHz, with temperature and VCC variation, the frequency would vary between 10 MHz and 4 MHz.
However, given silicon revisions and faster geometries, the oscillator was not redesigned to maintain an 8 MHz nominal frequency. Therefore, the upper frequency has been seen to be as much as 250% of the specified nominal frequency (20 MHz for an 8 MHz nominal frequency).
The same internal clock is used in both configuration (CCLK) and operational (OSC4/OSC5) modes; therefore, the OSC frequency can be easily determined by measuring the CCLK frequency during configuration.