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PROGRAMMING FOR THE
SYSTEM 1440
Computer interface to System 1440 is accomplished with a LeCroy 2132.
The language linking them has been designed to minimize programming
problems, however there are certain nuances that should not be forgot-
ten.
1. The mainframe select command is residual. It remains active until
another mainframe command is received. Obviously, if power is
turned off the 1440 will not be able to respond, it will also lose its
selected status when power is restored. Computer programs that are
waiting for responses should expect this situation and be able to cope
with it. Do not forget the mainframe select command when trying to
re-establish communications. This situation can also occur if the 1447
is plugged in, the 2132 cable is disconnected, or the 2132 is turned
off.
2. The 1440 may have mixed polarity and/or empty slots. This should be
taken into account since programming a card to the wrong voltage
will result in zero output. It is suggested that programming be done
by card or single channel. These are convenient sizes to be
compatible with both the 2132 buffer and the necessity to handle
polarity and empty slots.
3. To aid in determining the mainframe configuration, the unit will
generate a list of empty cards upon request. It the unit is full, a
response indicating that it is full will be sent. If not full the response
will be a variable length list (depending on setup). When is the list
ended? There are two ways to handle this. One is to consider that it
is certain to take less than 160 msec, between words. The other
would be to issue some other command (enable finished response for
example) and use that command's response as the list terminator.
4. LAMS. The 1440 generates an L1 with every transmission. This can
be used to indicate that the 2132 has received data. Unfortunately,
the LAM and the amount of data are uncorrelated. This raises the
question of when to clear the LAM. This can be difficult since
transfers occur in different sizes and the 2132 may be simultaneously
issuing new commands. If polling is acceptable it is recommended
that the LAM be ignored and allow the Q response from a F(2) to
indicate valid data. Note that L2 is NEVER generated.
5. FIFOs. Both the 2132 and the 1445 arc FIFO buffered. This allows a
burst of data to be transmitted at high speed, but then necessitates a
delay to allow processing of that data. The 2132 will indicate FIFO full
during a F16 by not returning a Q response. The 1445, being isolated
from the host computer cannot give such an indication. Its buffer
length exceeds that of the 2132 giving on level of protection. The best
way to ensure that no data is lost is to transmit data in a handshaking
mode. This means that data sent to the 1445 should be in blocks of
less than 40 words, the last word being a command that generates a
response.
This response will then have the additional meaning of "FIFOs
empty", thus ensuring proper operation. Normal program flow will
15
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