Radio Shack Telephone Interface II Technical Manual

A Level II
machine may
be identified
by a separate ROM
Board stuck
to the etch side
of the
CPU
Board. This Board
contains three
4K
ROMs,
a
TTL
decoder,
and a ribbon
cable. The cable attaches
the majority
of the ROM's
address
inputs and all
of the data outputs
to the now empty
main
Board ROM
sockets. There
is also
a 4-conductor ribbon
cable (green, orange,
red and yellow)
coming from
the
Level II Board. The
conductors connect
to the
CPU
Board
at A11, A12, A13
and ROM*. The
conductors
enable
a
BASIC I
to
BASIC
II
conversion on any level
production
Board to be quite painless.
A11 is used
as an address for all
three of
the ROM's. It is
tied to
pin
18 of Z1, Z2
and
Z3.
A12and
A13's leads
go to
the A0
and
A1 inputs
to decoder, Z4. Z4 is an addition to
the address decoder
network on the main
Board. When A12
and A13 is
00,
pin 1 of Z4
goes
low and ROM A is enabled.
When A12
and
A13
is
01,
ROM
B is selected; and when
A12 and A13 are
10,
ROM C is selected by
a
low
at
pin 3.
Since
we want the
ROM's
to be accessed only when the
CPU
needs instruction, ROM*
is therefore brought into
Z4
to
act
as a master enable. Only when ROM* is low will we
ever select
ROM A through ROM C. ROM power, minor
ROM
addressing and data output is handled by
the
large
ribbon cable. One end of this cable
will be placed
into
the
socket of
the ROM Board while the other
end
will be
attached in Z31's socket. Addressing
and data output are
handled
by the same circuits
that support
BASIC I.
29

Radio Shack Telephone Interface II Specifications

General

Brand	Radio Shack
Model	Telephone Interface II
Category	Desktop
Language	English