CDR-3250/80 TECHNICAL MANUAL
3-70 Issue 2.2
3-9.4 SRQ and Serial Poll Response. The receiver will
assert the Service Request uniline message (SRQ) when
any of several conditions occur. The status of each of
these conditions is given in the Serial Poll response byte.
The conditions and their location in the Serial Poll response
byte are shown in figure 3-11.
The Signal Present, Fault, and Local Control bits will
generate an SRQ on the bus whenever that state changes,
either from true to false or from false to true. Both Bad
Message and Bad Value bits are cleared upon receipt of a
valid command message.
When an SRQ message is received by the controller, each
device on the bus should be Serial Polled to determine
which device is requesting service. Bit 6, the SRQ bit will be
sent as true by any device that is currently asserting the
SRQ message. The controller may execute a Serial Poll with
the receiver at any time to read its status.
It is possible for an SRQ to be generated and for the Serial
Poll to show no change in status from previous polls. This
can happen if the state of a bit has changed and then
changed back before the poll is taken. For example, if a
signal is detected and then goes away before the poll is
read, the bit will still be read as false. This condition may be
detected by sending the SG? status request. The reply to
this status message is of the following form: SGbbbbbbbb
where each b character in the reply corresponds to a bit in
the serial poll response byte. If the b bit is a 1, that bit is the
one that caused the last SRQ message.
Each bit of the serial poll response byte may be masked off
to prevent it from generating an SRQ message on the bus.
This message is of the form: SMbbbbbbbb where each b is
replaced with a 1 to allow that bit to generate an SRQ or a
0 to 'mask off' that condition and prevent an SRQ from
being generated. For example to allow all conditions to
generate an SRQ except the Signal Present condition, send
SM11111110. The default (power-on) status of this message
is to allow all bits to generate an SRQ.
3-9.5 Device Clear And Selected Device Clear
Response. When the receiver receives the Device Clear
(DCL) command or the Selected Device Clear (SDC)
command, the receiver responds in the same way as if it
had received the K command. This command stops any
pending sweep or scan condition and places the receiver
into the normal state.
3-10 POWER UP AND TESTING
CONSIDERATIONS.
Whenever power is applied to the receiver it will execute a
Power On Self Test sequence. This sequence tests several
functions inside the receiver including memory tests, DSP
processor memory test, and a confidence test of the
configuration options stored in non-volatile memory, and
a BITE (built in test equipment) test of receiver functions.
If any of these tests fails, the receiver will not enter into
normal operation, but will wait for an operator action to
ensure that any failures will not go unnoticed. From the
front panel, the display will show the message "Hit any
Key to Continue". Since it is often required that the
receiver not send any unsolicited bus messages, receivers
configured with the serial interface will not announce this
wait condition over the bus. IEEE-488 units will assert the
SRQ line and set bit 3 of the Serial Poll response byte.
During this wait condition, the receiver will only respond to
a limited subset of commands from the bus. These are:
:? Request interface status message (serial only)
Serial Poll Sent in response to a SRQ (IEEE-488 only)
PO? Request results of Power On Self Test
! Clear wait condition and proceed with startup
For serial interface units in this wait condition, if the :?
command is sent, the receiver will respond with:
TE:EEPR or TE:POST
This indicates that the receiver is waiting. IEEE-488 units
will indicate this condition in bit 3 of the Serial Poll
response byte. This condition can only be cleared by
sending the ! command or by pressing any key on the
front panel. To determine the reason for POST failure, the
user should then request POST results (PO?) and if this
shows BITE failure, also request the BITE results (BI?)
after clearing the Power on Wait condition with the !
command.
The proper way to structure a remote control program to
handle this condition is to query each receiver for interface
status (:? or SRQ/Serial Poll) before sending any other
commands at power up and wait for the reply. A reply will
not be sent until a wait condition has been entered or
normal operation has been entered. If the wait condition is
indicated, send the ! command and test again. This process
should be repeated until the receiver responds with an
interface status other than TE: (serial interface) or shows
Serial Poll bit 3 clear (IEEE-488 interface).
Courtesy of http://BlackRadios.terryo.org
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