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has been completely read out. The wire ORed REQ lines are received by
the 4301 driver which waits for an adjustable delay (up to 0.5 microsec-
ond to be sure that all 4300Bs have finished conversion), then sends
REN to the first 4300B on the ECLbus. The data is then handshaked out
to the ECLbus using WST and WAK. After all data has been sent, REQ is
removed and PASS becomes a copy of REN.
If the first 4300 has not asserted REQ (there was no data above the
sparse scan threshold), then REN is simply copied to PASS. It is critical
that REN not be asserted until all 4300Bs have finished conversion,
because while REQ is not asserted, REN is simply copied to PASS.
If WST and WAK are used in the standard handshake mode, they control
the data flow. However, for high speed pipelined readout, WAK can be
jumpered to WST using the WSO and WAI connectors on the 4301
driver, effectively bypassing the handshake. The maximum ECLport rate
is achieved this way. In this case REN is used as the flow control.
Dropping REN effectively pauses the data flow. This works fine for the
4300B since there is only one data buffer. When REN returns, the data
flow resumes.
Modified Model 3377
FERA Behavior
The 3377 TDC begins conversion after the end of acquisition, after the
common stop or the common start time out. The conversion time is not
fixed however, it depends on the amount of data and the mode (single or
double word). The conversion time can be as short as two microseconds
or as long as 103 microseconds. In addition, the 3377 has a multi event
buffer, which can hold as many as 31 events. Fortunately, the 3377 can
also be operated in an unbuffered mode, which although slightly different
than the 4300B FERA ADC, is quite compatible with it.
In the multi buffer mode, REN is used as a token to read out one event
from each 3377. As soon as conversion starts, BUSY (REQ) is asserted.
BUSY is removed as soon as the event is safely stored in the buffer. If
REN arrives before conversion is complete (and no previous event is
waiting in the buffer) the module simply waits for an event to become
ready. When the event has been completely read out, PASS is asserted
and the module waits for REN to become false. Then PASS is set false
and the module is ready to read out the next event in the buffer. This
ensures that each event is read out completely before any part of the
next event is read. This use of REN as an event token is incompatible
with the use as a flow control device in the 4300B FERA system. Note
that REN can be asserted even before the event, the module simply
waits for the event.
4300B Compatible Mode
The single buffer mode is compatible with 4300Bs on the same ECLbus.
In this mode the BUSY signal becomes REQ. REQ can be delayed in
2 microsecond steps from 2 to 30 microseconds after the end of acquisi-
tion (the common stop, or the common start time out). REQ must not
come on before any 4300Bs on the ECLbus have finished conversion
and decided whether or not to assert REQ. REQ stays on until the data
has been read from the module. If REN arrives before conversion is
complete, the module waits for the event. During readout REN can be
used as flow control. After readout (and until the next conversion begins)
REN is simply copied to PASS. This allows REN to be used as flow
