P89LPC9102_9103_9107_3 © NXP B.V. 2007. All rights reserved.
Product data sheet Rev. 03 — 10 July 2007 45 of 61
NXP Semiconductors
P89LPC9102/9103/9107
8-bit microcontrollers with two-clock accelerated 80C51 core
9.4.5 Dual channel, continuous conversion mode
This is a variation of the auto scan continuous conversion mode where conversion occurs
on two user-selectable inputs. The result of the conversion of the first channel is placed in
result register, AD1DAT0. The result of the conversion of the second channel is placed in
result register, AD1DAT1. The first channel is again converted and its result stored in
AD1DAT2. The second channel is again converted and its result placed in AD1DAT3. An
interrupt is generated, if enabled, after every set of four conversions (two conversions per
channel).
9.4.6 Single step mode
This special mode allows ‘single-stepping’ in an auto scan conversion mode. Any
combination of the four input channels can be selected for conversion. After each channel
is converted, an interrupt is generated, if enabled, and the A/D waits for the next start
condition. May be used with any of the start modes.
9.5 Conversion start modes
9.5.1 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 A/D operating modes.
9.5.2 Start immediately
Programming this mode immediately starts a conversion. This start mode is available in all
A/D operating modes.
9.6 Boundary limits interrupt
The A/D converter has both a high and low boundary limit register. 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 are outside the limit an interrupt
will be generated, if enabled. If the conversion result is within the limits, the boundary
limits will again be compared after all 8 bits have been converted. An interrupt will be
generated, if enabled, if the result is outside the boundary limits. The boundary limit may
be disabled by clearing the boundary limit interrupt enable.
9.7 DAC output to a port pin with high output impedance
The A/D converter’s DAC block can be output to a port pin. In this mode, the AD1DAT3
register is used to hold the value fed to the DAC. After a value has been written to the DAC
(written to AD1DAT3), the DAC output will appear on the channel 3 pin.
9.8 Clock divider
The A/D converter requires that its internal clock source be in the range of 500 kHz to
3.3 MHz to maintain accuracy. A programmable clock divider that divides the clock
from 1 to 8 is provided for this purpose.
