8-bit microcontroller with accelerated two-clock 80C51 core
8.23 Analog comparators
Two analog comparators are provided on the P89LPC933/934/935/936. Input and output
options allow use of the comparators in a number of different configurations. Comparator
operation is such that the output is a logic 1 (which may be read in a register and/or routed
to a pin) when the positive input (one of two selectable pins) is greater than the negative
input (selectable from a pin or an internal reference voltage). Otherwise the output is a
zero. Each comparator may be configured to cause an interrupt when the output value
The overall connections to both comparators are shown in Figure 21. The comparators
function to VDD = 2.4 V.
When each comparator is first enabled, the comparator output and interrupt flag are not
guaranteed to be stable for 10 microseconds. The corresponding comparator interrupt
should not be enabled during that time, and the comparator interrupt flag must be cleared
before the interrupt is enabled in order to prevent an immediate interrupt service.
When a comparator is disabled the comparator’s output, COn, goes HIGH. If the
comparator output was LOW and then is disabled, the resulting transition of the
comparator output from a LOW to HIGH state will set the comparator flag, CMFn. This will
cause an interrupt if the comparator interrupt is enabled. The user should therefore
disable the comparator interrupt prior to disabling the comparator. Additionally, the user
should clear the comparator flag, CMFn, after disabling the comparator.
Fig 21. Comparator input and output connections
8.23.1 Internal reference voltage
An internal reference voltage generator may supply a default reference when a single
comparator input pin is used. The value of the internal reference voltage, referred to as
Vref(bg), is 1.23 V ± 10 %.
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 8 — 12 January 2011
© NXP B.V. 2011. All rights reserved.
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