80C550 Datasheet, PDF (10/28 Pages) NXP Semiconductors – 80C51 8-bit microcontroller family 4K/128 OTP/ROM/ROMless, 8 channel 8 bit A/D, watchdog timer

Philips Semiconductors
80C51 8-bit microcontroller family
4K/128 OTP/ROM/ROMless, 8 channel 8 bit A/D, watchdog timer
Product specification
80C550/83C550/87C550
A/D CONVERTER PARAMETER DEFINITIONS
The following definitions are included to clarify some specifications
given and do not represent a complete set of A/D parameter
definitions.
Absolute Accuracy Error
Absolute accuracy error of a given output is the difference between
the theoretical analog input voltage to produce a given output and
the actual analog input voltage required to produce the same code.
Since the same output code is produced by a band of input voltages,
the “required input voltage” is defined as the midpoint of the band of
input voltage that will produce that code. Absolute accuracy error
not specified with a code is the maximum over all codes.
Nonlinearity
If a straight line is drawn between the end points of the actual
converter characteristics such that zero offset and full scale errors
are removed, then non-linearity is the maximum deviation of the
code transitions of the actual characteristics from that of the straight
line so constructed. This is also referred to as relative accuracy and
also integral non-linearity.
Differential Non-Linearity
Differential non-linearity is the maximum difference between the
actual and ideal code widths fo the converter. The code widths are
the differences expressed in LSB between the code transition
points, as the input voltage is varied through the range for the
complete set of codes.
Gain Error
Gain error is the deviation between the ideal and actual analog input
voltage required to cause the final code transition to a full-scale
output code after the offset error has been removed. This may
sometimes be referred to as full scale error.
Offset Error
Offset error is the difference between the actual input voltage that
causes the first code transition and the ideal value to cause the first
code transition. This ideal value is 1/2 LSB above V_ref–.
Channel to Channel Matching
Channel to channel matching is the maximum difference between
the corresponding code transitions of the actual characteristics
taken from different channels under the same temperature, voltage
and frequency conditions.
Crosstalk
Crosstalk is the measured level of a signal at the output of the
converter resulting from a signal applied to one deselected channel.
Total Error
Maximum deviation of any step point from a line connecting the ideal
first transition point to the ideal last transition point.
Relative Accuracy
Relative accuracy error is the deviation of the ADC’s actual code
transition points from the ideal code transition points on a straight
line which connects the ideal first code transition point and the final
code transition point, after nullifying offset error and gain error. It is
generally expressed in LSBs or in percent of FSR.
WATCHDOG TIMER
The purpose of the watchdog timer is to reset the microcontroller
within a reasonable amount of time if it enters an erroneous state,
possibly due to a programming error, electrical noise, or RFI. When
enabled, the watchdog circuit will generate a system reset if the user
program fails to “feed” (or reload) the watchdog within a
predetermined amount of time.
The watchdog timer implemented on the 8XC550 has a
programmable interval and can thus be fine tuned to a particular
application. If the watchdog function is not used, the timer may still
be used as a versatile general purpose timer.
The watchdog function consists of a programmable 13-bit prescaler,
and an 8-bit main timer. The main timer is clocked by a tap taken
from one of the top 8 bits of the prescaler. The prescaler is
incremented once every machine cycle, or 1/12 of the oscillator
frequency. Thus, the main counter can be clocked as often as once
every 64 machine cycles or as seldom as once every 8192 machine
cycles.
When clocked, the main counter decrements. If the main watchdog
counter reaches zero, a system reset will occur. To prevent the
watchdog timer from under-flowing, the watchdog must be fed
before it counts down to zero. When the watchdog is fed, the
contents of the WDL register are loaded into the main watchdog
counter and the prescaler is cleared.
WDCON Register
MSB
LSB
PRE2 PRE1 PRE0
X
X
WDRUN WDTOF WDMOD
Symbol Position Function
WDCON.7 PRE2 Prescaler select (read/write).
WDCON.6 PRE1 These bits select theprescaler divide ratio
WDCON.5 PRE0 according to the following table:
PRE2
PRE1
PRE0
DIVISOR (FROM f_OSC)
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
12 × 64
12 × 64 × 2
12 × 64 × 4
12 × 64 × 8
12 × 64 × 16
12 × 64 × 32
12 × 64 × 64
12 × 64 × 128
WDCON.4 –
Not used
WDCON.3 –
Not used
WDCON.2 WDRUN Run control (read/write).
This bit turns the timer on (WDRUN = 1) or off
(WDRUN = 0) if the timer mode has been
selected.
WDCON.1 WDTOF Timeout flag (read/write).
This bit is set when the watchdog timer
underflows. It is cleared by an external reset
and can be cleared by software.
WDCON.0 WDMOD Mode selection (read/write).
When WDMOD = 1, the watchdog is selected;
when WDMOD = 0, the timer is selected.
Selecting the watchdog mode automatically
disables power-down mode. WDMOD is
cleared by external reset. Once the watchdog
mode is selected, this bit can only be cleared
by writing a 0 to this bit and then performing a
feed operation.
1998 May 01
10