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GLOSSARY/SYMBOLS, TERMS, AND DEFINITIONS
1–34
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O
OCF:
Opcode Fetch. Goes low at the beginning of a memory read operation that fetches the first byte of an instruc-
tion. It then resumes its high level at the end of the opcode fetch(es).
offset:
A signed value that is added to the base operand to give the final address
opcode:
combination of operands. Some TMS370 instructions use 16-bit opcodes.
Operation code.The first byte of the machine code that describes to the CPU the type of operation and
operand:
The part of an instruction that tells the programmer where the CPU will fetch or store data
one-time programmable (OTP) read-only memory:
have the data content of each memory cell altered once. Also referred to as OTP.
a read-only memory that, after being manufactured, can
Output Enable:
causes the output to assume a high-impedance state. (See also chip select.)
A control input that, when true, permits data to appear at the memory output, and when false,
P
PACT:
Programmable acquisition and control timer module.A timer coprocessor module for the TMS370 microcon-
troller family.
PDIP:
Plastic Dual In-Line Package
peripheral file (PF):
on-board peripherals and system configuration
The 128 or 256 bytes of memory, starting at 1000h, that contain the registers that control the
peripheral-file frames:
A set of sixteen contiguous peripheral file registers, usually related by function
PLCC:
Plastic Leaded Chip Carrier
PPM:
Pulse-position modulation.A serial signal in which the information is contained in the frequency of a signal
with a constant-pulse width. By using the timer-compare features, a TMS370 device can output a PPM signal with
a constant duty cycle without any program intervention.
prescaler:
ing source by a factor of 4, 16, 64, or 256.
A circuit that slows the rate of a clocking source to the counter. The timer 1 prescaler can slow the clock-
privilege mode:
bits. Once the privilege mode is disabled, these registers cannot be changed before another reset. This mode
does not affect the EEPROM or the watchdog registers.
A mode immediately following reset in which the program can alter the privileged registers and
program:
stored into various desired locations in a previously erased device
Typically associated with EPROM and OTP memories, the procedure whereby logical 0s (or 1s) are
program counter (PC):
A CPU register that identifies the current statement in the program
prototyping device:
size, and timings to those of the actual device. Programmable memory such as EEPROM or EPROM is used in
place of the masked ROM.
A device used before mask-ROM devices are available that has identical functions, pinout,
PSDIP:
Plastic Shrink Dual In-Line Package
pulse accumulation:
T1EVT or T2EVT signal
A timer 1 or timer 2 mode that keeps a cumulative count of SYSCLK pulses gated by the
PWM:
Pulse-width modulation.A serial signal in which the information is contained in the width of a pulse of a
constant-frequency signal. By using the timer-compare features, a TMS370 device can output a PWM signal with
a constant-duty cycle without any program intervention.