IBM Series 1 User Manual page 111

Applicati.Q!!
~ummp.I.I
The following are examples of how the timer feature can be
used. The X appearing after the word timer denotes either
timer 0 or timer 1.
High
Accura£Z Q!: Non-standard
Fre-g:uen~y
£m!!!ting. To utili-ze
a clock of any arbitrary accuracy or frequency up to 1 MHz,
the timer X customer clock input should be used, and the
timer mode controls set to select customer time base.
Pul~~
2£:
EV~!
f.2..!!!!tillil. The timer X customer clock input
should be used, and the timer mode controls set to select
customer time base. The number of pulses recorded prior to
an interrupt being posted is dependent on the value set into
the timer and the chosen run mode. For example, if the
timer (and thus the auto-load register) were set to all
zeros, and the chosen run mode was periodic, the timer would
interrupt on each pulse counted. If under these same
conditions, the timer was set to 100, i t would interrupt on
every 101st pulse. Pulses are recorded and interrupts
generated at the leading (passive to active) edge of the
pulse. Also, except for power-on reset, every pulse is
counted only once even though the timers could be stopped
and started many times during the active duration of a given
pulse. Note that duty-cycle constraints on pu.lse inputs for
the customer clock input do not preclude pulses of very lov
frequency or even pulses vith a random duty cycle.
Pul.§~ Duratiol!, Counting. The timer X external gate input
should be used for the pulse whose duration is being
measured. A standard internal time base can be used. A
clock of arbitrary accuracy or frequency can also be used
and connected to the timer X customer clock input. The
timer mode controls should be set to arm the external gate
and to select the time base desired. The measure of the
pulse duration is a function of (1) the initial and end
values of the timer, (2) a known time base, (3) the type of
interrupt returned, and (4) the run mode used. The customer
should ensure that the external gate input is inactive
before the timer is set to run state, or an error in
measuring viII occur. The outputs from the timer card are
available for this purpose. For example, assume clock
inputs were occurring every 1 microsecond and an initial
value of 1000 was loaded into the timer. The external gate
input going active causes the timer to start. When the
external gate goes inactive, the timer stops and an
attention interrupt occurs. The timer is read and
it
is
found to contain a value of 500. Therefore, the pulse width
of the external gate pulse vas 500 microseconds ±1.
3-4 GA34-0033
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