P89LPC952_954_4 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 04 — 24 July 2008 49 of 69
NXP Semiconductors
P89LPC952/954
8-bit microcontroller with 10-bit ADC
8.4.6 Single step mode
This special mode allows ‘single-stepping’ in an auto scan conversion mode. Any
combination of the eight input channels can be selected for conversion. After each
channel is converted, an interrupt is generated, if enabled, and the ADC waits for the next
start condition. May be used with any of the start modes.
8.5 Conversion start modes
8.5.1 Timer triggered start
An A/D conversion is started by the overflow of Timer 0. Once a conversion has started,
additional Timer 0 triggers are ignored until the conversion has completed. The Timer
triggered start mode is available in all ADC operating modes.
8.5.2 Start immediately
Programming this mode immediately starts a conversion. This start mode is available in all
ADC operating modes.
8.5.3 Edge triggered
An A/D conversion is started by rising or falling edge of P1.4. Once a conversion has
started, additional edge triggers are ignored until the conversion has completed. The edge
triggered start mode is available in all ADC operating modes.
8.6 Boundary limits interrupt
The ADC has both a high and low boundary limit register. The user may select whether an
interrupt is generated when the conversion result is within (or equal to) the high and low
boundary limits or when the conversion result is outside the boundary limits. An interrupt
will be generated, if enabled, if the result meets the selected interrupt criteria. The
boundary limit may be disabled by clearing the boundary limit interrupt enable.
An early detection mechanism exists when the interrupt criteria has been selected to be
outside the boundary limits. In this case, after the four MSBs have been converted, these
four bits are compared with the four MSBs of the boundary high and low registers. If the
four MSBs of the conversion meet the interrupt criteria (i.e., outside the boundary limits)
an interrupt will be generated, if enabled. If the four MSBs do not meet the interrupt
criteria, the boundary limits will again be compared after all 8 MSBs have been converted.
A boundary status register (BNDSTA0) flags the channels which caused a boundary
interrupt.
8.7 Clock divider
The ADC requires that its internal clock source be in the range of 320 kHz to 9 MHz to
maintain accuracy. A programmable clock divider that divides the clock from 1 to 8 is
provided for this purpose.
8.8 Power-down and Idle mode
In Idle mode the ADC, if enabled, will continue to function and can cause the device to exit
Idle mode when the conversion is completed if the A/D interrupt is enabled. In
Power-down mode or Total Power-down mode, the ADC does not function. If the ADC is
enabled, it will consume power. Power can be reduced by disabling the ADC.
