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8XC251SA, SB, SP, SQ USER’S MANUAL
Glossary-6
set The term set refers to the value of a bit or the act of
giving it a value. If a bit is set, its value is “1”; setting
a bit gives it a “1” value.
SFR Special-function register.
sign extension A method for converting data to a larger format by
filling the extra bit positions with the value of the
sign. This conversion preserves the positive or
negative value of signed integers.
sink current Current flowing into a device to ground. Always a
positive value.
source-code compatibility The ability of an MCS 251 microcontroller to execute
recompiled source code written for an MCS 51 micro-
controller.
source current Current flowing out of a device from V
CC
. Always a
negative value.
source mode An operating mode that is selected by a configuration
bit. In source mode, an MCS 251 microcontroller can
execute recompiled source code written for an MCS
51 microcontroller. In source mode, the MCS 251
microcontroller cannot execute unmodified binary
code written for an MCS 51 microcontroller. See
binary mode.
SP Stack pointer.
SPX Extended stack pointer.
state time (or state) The basic time unit of the device; the combined
period of the two internal timing signals, PH1 and
PH2. (The internal clock generator produces PH1 and
PH2 by halving the frequency of the signal on
XTAL1.) With a 16-MHz crystal, one state time
equals 125 ns. Because the device can operate at
many frequencies, this manual defines time require-
ments in terms of state times rather than in specific
units of time.
UART Universal asynchronous receiver and transmitter. A
part of the serial I/O port.
WDT Watchdog timer, an internal timer that resets the
device if the software fails to operate properly.