Omron CPM1

Glossary
505
refresh The process of updating output status sent to external devices so that it agrees
with the status of output bits held in memory and of updating input bits in memory
so that they agree with the status of inputs from external devices.
relay-based control The forerunner of PCs. In relay-based control, groups of relays are interconnect-
ed to form control circuits. In a PC, these are replaced by programmable circuits.
reserved bit A bit that is not available for user application.
reserved word A word in memory that is reserved for a special purpose and cannot be accessed
by the user.
reset The process of turning a bit or signal OFF or of changing the present value of a
timer or counter to its set value or to zero.
response code A code sent with the response to a data transmission that specifies how the
transmitted data was processed.
response format A format specifying the data required in a response to a data transmission.
response monitoring time The time a device will wait for a response to a data transmission before assum-
ing that an error has occurred.
Restart Bit A bit used to restart part of a PC.
result word A word used to hold the results from the execution of an instruction.
retrieve The processes of copying data either from an external device or from a storage
area to an active portion of the system such as a display buffer. Also, an output
device connected to the PC is called a load.
retry The process whereby a device will re-transmit data which has resulted in an er-
ror message from the receiving device.
return The process by which instruction execution shifts from a subroutine back to the
main program (usually the point from which the subroutine was called).
reversible counter A counter that can be both incremented and decremented depending on the
specified conditions.
reversible shift register A shift register that can shift data in either direction depending on the specified
conditions.
right-hand instruction See terminal instruction.
rightmost (bit/word) The lowest numbered bits of a group of bits, generally of an entire word, or the
lowest numbered words of a group of words. These bits/words are often called
least-significant bits/words.
rising edge The point where a signal actually changes from an OFF to an ON status.
ROM Read only memory; a type of digital storage that cannot be written to. A ROM
chip is manufactured with its program or data already stored in it and can never
be changed. However, the program or data can be read as many times as de-
sired.
rotate register A shift register in which the data moved out from one end is placed back into the
shift register at the other end.
RS-232C interface An industry standard for serial communications.
RUN mode The operating mode used by the PC for normal control operations.