Digital
Circuitry
Serial Interface
Board
A16
(optional) 0
GPIB Interface
Board
Al
7 (optional) 0
3-
30
The
serial interface has two major components: a 5 Volt to
+/-10
Volt
converter U2201 and
the
RS232 driver receiver
IC
U2200.
The
TXD,
RXD
and CTS lines
which
are available at
the
connector J1504 at
A15 are UART lines
of
the 68070. DSR,
DTR
and
RTS are connected to the
68070 through latches (diagram 21).
The presence of the serial interface option board can
be
detected
by
the
microprocessor by monitoring the SERINST line.
The
GPIB
board contains a TMS9914A
GPIB
communication
chip
(U2300),
which is connected to the lower
half
of the databus BUFD[0
..
7),
and
the
address lines PROA[l..3]
of
the 68070. Combined with the
chip
select line
GPIBL
it is therefore memory mapped
in
the
odd hexadecimal addresses
300001-30000F. The clocking of
the
TMS9914A is
done
with
the
CLK5M
clock. Pin 39
of
the TMS9914A is wired to the trigger circuitry
of
the
A10
board to enable triggering of the instrument on
GPIB
interface messages.
02301
and
02302 are standard
GPIB
driver-receiver chips.
The
presence of the
GPIB
interface option board can be detected
by
the
microprocessor by monitoring the GPIBINST line.
Theory
of
Operation
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