P87C554 NXP Semiconductors, P87C554 Datasheet - Page 28

• Manufacturer Part Number: P87C554
• Description: The P87C554 Single-Chip 8-Bit Microcontroller is manufactured inan advanced CMOS process and is a derivative of the 80C51microcontroller family
• Manufacturer: NXP Semiconductors

between AVref+ and AVref–. If the analog input voltage range is from
Philips Semiconductors
10-Bit ADC Resolution and Analog Supply: Figure 24 shows how
the ADC is realized. The ADC has its own supply pins (AV
AV
DAC’s resistance-ladder. The ladder has 1023 equally spaced taps,
separated by a resistance of “R”. The first tap is located 0.5 x R
above Vref–, and the last tap is located 1.5 x R below Vref+. This
gives a total ladder resistance of 1024 x R. This structure ensures
that the DAC is monotonic and results in a symmetrical quantization
error as shown in Figure 26.
For input voltages between Vref– and (Vref–) + 1/2 LSB, the 10-bit
result of an A/D conversion will be 00 0000 0000B = 000H. For input
voltages between (Vref+) – 3/2 LSB and Vref+, the result of a
conversion will be 11 1111 1111B = 3FFH. AVref+ and AVref– may
be between AV
positive with respect to AVref–, and the input voltage (Vin) should be
2 V to 4 V, then 10-bit resolution can be obtained over this range if
AVref+ = 4V and AVref– = 2 V.
The result can always be calculated from the following formula:
2002 Mar 25
80C51 8-bit microcontroller – 12 clock operation
16K/512 OTP/RAM, 8 channel 10-bit A/D, I
capture/compare, high I/O
SS
Result + 1024
TOTAL RESISTANCE
=
=
) and two pins (Vref+ and Vref–) connected to each end of the
1023R + 2 x R/
1024R
DD
+ 0.2 V and AV
R/2
R
R
R
R
R
R/2
AV
V
ref)
IN
* AV
AV
AV
* AV
ref+
ref–
ref*
SS
ref*
– 0.2 V. AVref+ should be
Value 0000 0000 00
Value 1111 1111 11
V
V
ref
in
Figure 24. ADC Realization
DD
COMPARATOR
and
–
+
2
is output for voltages V
is output for voltages (V
C, PWM,
1023
1022
1021
3
2
1
0
DECODER
26
Power Reduction Modes
The P87C554 has two reduced power modes of operation: the idle
mode and the power-down mode. These modes are entered by
setting bits in the PCON special function register. When the
P87C554 enters the idle mode, the following functions are disabled:
CPU
Timer T2
PWM0, PWM1
ADC
In idle mode, the following functions remain active:
Timer 0
Timer 1
Timer T3
SIO0 SIO1
External interrupts
When the P87C554 enters the power-down mode, the oscillator is
stopped. The power-down mode is entered by setting the PD bit in
the PCON register. The PD bit can only be set if the EW input is tied
HIGH.
ref–
ref+
to (V
APPROXIMATION
– 3/2 LSB) to V
SUCCESSIVE
REGISTER
ref–
MSB
LSB
+ 1/2 LSB)
(halted)
(halted and reset)
(reset; outputs are high)
(may be enabled for operation in Idle mode
by setting bit AIDC (AUXR1.6) ).
ref+
APPROXIMATION
CONTROL LOGIC
SUCCESSIVE
P87C554
Product data
SU00961
START
READY