Amplicon Liveline PC27E, Инструкция по эксплуатации

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PC27E Page 11
4.4.2 Frequency Measurements
A simple Frequency Counter can be implemented using the external frequency output on
connector SK1 pin 1.
The output of Counter 0 is inverted by QA12-B, and then fed to the gate of counter 2 by
positioning jumper J7 to /OUT0 (upper position). Therefore Counter 0 controls the gate of
Counter 2 and, if Counter 0 is programmed for Mode 2 (terminal count), a fixed-length gate
pulse can be created for Counter 2.
The external signal (of unknown frequency) can be connected to SK1 pin 1 and jumpered into
the clock of counter 2 by positioning J4 in the lower position. If programmed to count down
from HexFFFF, Counter 2 will count the number of external clock cycles during its gate pulse.
Since the gate pulse is of known duration, the number of external clock cycles per second can
be calculated, and hence the frequency.
4.5 Wait State Generator Setting (Option)
The PC27E incorporates an on-board wait state generator (QA10) to enable it to operate
reliably in a wide range of PC/XT/AT and ISA machines. The need for this is because some
machines, that are otherwise IBM compatible, now operate the I/O expansion bus at clock
frequencies higher than the 8MHz specified in the ISA standard. This option is not fitted as
standard.
Many interface ICs currently available cannot operate at these higher frequencies and it
becomes necessary to slow down the bus interface signals, locally, on the PC27E board. The
degree of retardation can be adjusted to give optimum performance in any machine. Being
local to the PC27E board, this slowing down in no way impairs the performance of the host
computer.
The expansion bus frequency is not necessarily the same as that of the main processor clock.
A computer which is specified as a 12 or 16 MHz machine could well have an expansion bus
frequency of 8MHz. Unless explicitly stated in the machine specification there is no easy way
to establish the speed of the expansion bus. If the expansion speed is known, then use Table
2 to set the appropriate number of wait states. If the bus speed is not known, it is suggested
that the number of wait states is left at zero (No jumper). If the PC27E functions correctly
leave the setting at zero wait states. If operation is erratic, increase the number of wait states.
Introducing wait states can cause some machines to hang up, otherwise no harm can be
done by setting the number of wait states too high, however the response of the PC27E board
will not be optimum.
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2
2
2
TABLE 2 SETTINGS FOR WAIT STATE GENERATOR