ZiLOG Z80 Handbook page 261

DIGITAL GROUP MEMORY BOARDS
Two types of 8K memory boards are available, both using 2102
static RAM memory chips. One version is a 500-nanosecond mem-
ory, while the other board is a low-power 250-nanosecond memory.
No wait states are required for the Z-80 CPU with the 500-nano-
second version. A 1702A EPROM board holds 4K bytes of 1702A
EPROM memory (16 chips as the 1702 is a 256-byte EPROM chip).
DIGITAL GROUP I/O INTERFACES AND DEVICES
An Input/Output Board provides four 8-bit input ports and four
8-bit latching output ports. The I/O board supports either a mem-
ory-mapped I/O scheme as in the Motorola 6800 microprocessor,
or the 8080/Z-80 I/O mapped scheme. (In the memory-mapped
scheme, I/O devices are not addressed by I/O instructions but as
16-bit addresses).
A TV Readout and Audio-Cassette Interface Board allows both
a character-oriented tv display and audio-cassette recording and
playback. The TV Readout portion of the board provides a 64-
character by 16-line display with a 7- by 9-dot matrix display of
characters. The board will store the 1K characters in on-board RAM
storage. One hundred twenty eight ASCII characters are display-
able including both upper- and lower-case alphabets, numbers,
extended math symbols, and Greek alphabet. The cursor may be
positioned forward and backward under software control. Output
of the tv section of the board is to a standard monitor (Digital Group
or others) or to a standard television with input to the video section.
The Audio-Cassette portion of the board records, or reads, data
on standard Phillips-type audio-cassette recorders using FSK (fre-
quency-shift keying) recording. Data rates are 1100 baud which is
the equivalent of 100 characters per second, approximately 10 times
faster than a standard teletypewriter.
A separate Cassette-Storage System is also available, using one
to four Phi-Deck cassette transports. The Phi-Deck is a quality
audio-cassette drive with a file-search capability and other func-
tions. Data rates are 800 bytes per second (!) and a search speed
of 100 inches per second. A software operating system (driver) is
supplied to implement recording of multiple blocks, single blocks,
reading, CRC check, fast reverse and forward, and block search.
The Cassette-Storage System requires a Phi-F interface board, and
either a two- or four-drive cabinet with transports.
Another peripheral and interface offered is the Digital Group
96-Column Impact Printer. This is a relatively inexpensive 120
character per second, 96 character per line printer that prints on
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