switch and a second IMP8980D for
communication with the line interface
circuits.
A larger digital switching system may be
designed by cascading a number of
IMP8980Ds.
Figure 9
shows four
IMP8980Ds arranged in a non-blocking
configuration which can switch any
channel on any of the ST-BUS inputs to
any channel on the ST-BUS outputs.
Application Circuit with 6802
Processor
Figure 10
shows an example of a
complete circuit which may be used to
evaluate the chip.
For convenience, a 4MHz crystal
oscillator has been used rather than a
4.096MHz clock, as both are within the
limits of the chip’s specifications. The RC
delay used with the 393 counters ensures a
sufficient hold time for the FP signal, but
the values used may have to be changed if
faster 393 counters become available.The
chip is shown as memory mapped into the
MEK6802D3 system. Chip addresses
00-3F correspond to processor addresses
2000-203F. Delay through the address
decoder requires the VMA signal to be
used twice to remove glitches. The
MEK6802D3 board uses a 10KΩ pullup
on the MR pin, which would have to be
incorporated into the circuit if the board
was replaced by a processor.
Figure 6 - Connection Memory Low Bits
Stream
Address
Bits
Channel
Address
Bits
}
7
6
5
BIT
7-5*
NAME
Stream *
Address
Bits
Channel
Address
Bits*
4-0*
DESCRIPTION
The number expressed in binary notation on these 3 bits is
the number of the ST-BUS stream for the source of the connection.
Bit 7 is the most significant bit. e.g., if bit 7 is 1, bit 6 is 0 and bit 5
is 0, then the source of the connection is a channel on STi4.
The number expressed in binary notation on these 5 bits is
the number of the channel which is the source of the connection
(The ST-BUS stream where the channel lies is defined by bits 7,
6 and 5.). Bit 4 is the most significant bit. e.g., if bit 4 is 1, bit 3 is
0, bit 2 is 0, bit 1 is 1 and bit 0 is 1, then the source of the
connection is channel 19.
* If bit 2 of the corresponding Connection High location is 1 or if bit 6 of the Control Register is 1,
then the entire 8 bits are output on the channel and stream associated with this location.
Otherwise, the bits are used as indicated to define the source of the connection which is
output on the channel and stream associated with this location.
}
4
3
2
1
0
5
IMP [ IMP, INC ]
