Apple Lisa - Page 62

Confidential
Lisa Hardware Reference Manual 7-Jul-81
Modem Modulator/Demodulator. To send digital data over a
telephone line, the Modem transforms the bit patterns'
into a stream of modulations of a carrier signal. At
the receiving end, the signal is demodulated to recover
the data.
MMU Memory Management Unit
ms millisecond.
N-key rollover Nearly all keyboard interfaces work by scanning the keys
and forming a
two dimensional matrix representation of the
state of the keys. The logic involved can tell when two
keys are being pressed simultaneously (rollover), but
Nibble
~I
ns
Page
when three or more keys are held down, phantom keys
can appear (there are hidden paths through the logic array).
N-key rollover design adds a diode in series with every
key switch to eliminate the hidden paths.
A set of bits smaller than a byte. On the Lisa,
a nibble is 4 bits..
Non-Maskable Interrupt. When the prQcessor receives
an interrupt, it usually checks a mask to see whether
it should pass control to that interrupt's handler.
A non-maskable interrupt is always honored.
nanosecond. A billionth of a s~cond. Also abbreviated
as nsee.
512 bytes
Parameter memory
Parity
PC
Pll
PIPPIN
Port
A non-volatile block of RAM set aside for such things
as the system serial number, configuration data, and
user-defined information.
Parity has to do with the number of one bits in a word.
If there are an even number, the word has even parity.
Parity can be checked to insure that one bit in a word
has not been incorrectly flipped during transmission.
Program Counter
Peripheral Interface Adapter (6522 on the Lisa)
A sealed 5 megabyte hard disk made by Apple
An I/O location.
Page 62