
Glossary
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automatic, the boot program will be loaded to the RAM from the EPROM upon
power up or reset. Programs can be read from and written to the EPROM with
the LOAD and SAVE commands, respectively.
execution sequence
The order of operation in which the PC and ASCII Unit hardware execute their
respective programs.
flag
A hardware flag is a bit that is set or cleared by the machine to indicate a particu-
lar state or condition of the Unit to a peripheral device or to the program. Exam-
ples of PC hardware flags are the Read and Write flags. A software flag is set or
cleared by the user to indicate to the hardware a particular choice or option. For
instance, software flags are sometimes used for setting the direction of data
transfer or the baud rate of a communication device.
hexadecimal
Hexadecimal or hex is a numerical system based on the number 16. One hex
digit can be represented by four binary digits in the range of zero to 15. The num-
bers 10 through 15 are represented by the letters A through F, respectively.
index register
One of the microprocessor’s hardware registers. It is used for assembly lan-
guage programming.
interrupt number
A code that is sent from the interrupting device to the microprocessor indicating
which device is “calling.” The interrupt number is especially important if there is
more than one peripheral device connected to a microprocessor.
interrupt
A signal sent to the microprocessor from a peripheral device that causes the mi-
croprocessor to alter its normal processing routine. An interrupt says to the mi-
croprocessor, “stop what you’re doing and pay attention to me !” When an inter-
rupt is acknowledged by the microprocessor, program execution will branch to
an interrupt service routine specifically written to handle the given interrupt.
I/O device
I/O stands for input/output. Some examples of I/O devices are printers, mo-
dems, fax machines, and display terminals.
machine no. switch
Used to select the unit number for the allocation of PC words. The Machine No.
switch is located on the front panel of the ASCII Unit.
mantissa
The part of a numerical expression to the right of the decimal point.
memory area designator (@) A parameter of the PC READ and PC WRITE statements used to access specif-
ic PC data areas. When using the memory area designator for data transfer, the
ASCII Unit does not need an accompanying PC data transfer routine.
monitor mode
The mode or environment where assembly language programs are written,
edited, and tested.
monitor mode commands
The commands used in monitor mode for writing, editing, and debugging an as-
sembly language program.
MSB/LSB
MSB stands for Most Signicant Byte and refers to the upper or left half of a data
word ( a data word contains two bytes ). The Least Significant Byte refers to the
lower or right half of a data word.
octal
A numerical system based on the number eight. One octal digit is made up of
three binary digits in the range of zero to seven.
parameter/argument
A parameter is a value or symbol supplied to a BASIC or assembly language
command. A parameter either directs a command to implement a particular op-
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