Manual

15-4 Appendix E
CASE II -- STEADY STATE
A B C D E F
--host--> -- next-move ...
 comp   host comp
-RS-232C->
 xmit 
-precomp->
 
-Wait->
 
... previous move execution ---------->-3 mSec->-- move ...
 exec.
This case is similar to the first, with the addition of the delay between time D and time E,
during which the Automove System waits for the physical execution of the previous move to
complete. The last 3 milliseconds of precomputation cannot occur until after E. As long as
the typical move execution time exceeds the total from A through D, the system throughput
is solely determined by the move length, the acceleration, and the slew stepping rate.
Of course, the typical application falls somewhere between the two cases. Time A-B is the
least controllable element; if the host is very slow, each move is performed as a Case I move.
Depending on host software, time A-B may depend on how long the host takes to produce
each ASCII character from its internal numerical representation, how fast its disk drive is,
and so on.
Time B-C depends on the baud rate, on whether a parity bit is being used, on the number of
stop bits, and, perhaps most importantly, on how many "garbage" characters the host sends
with each numeric parameter. If the host sends ten digits after the decimal point, or precedes
each parameter with many blanks to make the "columns" line up as on a printer, throughput
will suffer. For short vectors on most areas of the platen, the MR command requires fewer
digit characters than MA, since the MR parameters tend to be smaller numbers. See
Chapter 5 for recommendations on baud rate, parity, and stop bits.
Time C-D is fairly constant; it is usually in the range 10 through approximately 50
milliseconds. The worst case for vectors is where the following all happen at once: a burst
of characters is being received during the precomputation for an MR command; and the MR
parameters are negative and have digits after the decimal point.
If, for some reason, the host asks the Automove System to output something after each
vector or arc, no overlap is possible. This is because the host must typically await the
response before sending the next command. Also, most ACL output requests are not
processed until the end of the preceding move. (Exceptions: OC, OE, OL, and OO do not
wait.) The unsolicited "?" response to errors and Emergency Stops is intended to eliminate
most of the need for this situation. See Exceptional Conditions in Chapter 5.