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|  MIL-D-81347C(AS)
(2) The four input/output channels associated with each chan-
nel group, in order of descending priority are: Channel 3, Channel 2, Channel 1, and Channel 0. The
Computer 1/0 Channel numbers, listed in reference with its respective I/O Group, and Channel within
the I/O Group are specified in Table 1-4.
2.2
Input/Output Timing
2.2.1
Input Timing Considerations
2.2.1.1
Data Inputs to Computer from Peripheral Equipment - The input
Data Request signal indicates to the computer that data has be en placed on the 3 0 datelines. The In-
put Data Request must be maintained on the lines until an Input Acknowledge is received. As shown in
Figure 1-3, there is a 7.75(-0.47) microsecond minimum delay between the setting of the Input Data
Request and its answering Input Acknowledge. There is no maximum limit on the duration of the Input
Data Request since its value for any particular cycle is determined by the interaction with the com-
puter program and the other input/output channels. The data lines must remain stable as long as the
Input Data Request is set.
The Input Acknowledge indicates to the peripheral equipment
that its 30 datelines have been sampled. The Input Acknowledge signal is set for a fixed time inter-
val. The peripheral equipment must be capable of detecting as an Input Acknowledge a signal which
may exist in the stable "1" state for as little as 2.5 (0.15) microseconds Upon sensing the Input
Acknowledge, the Input Data Request may be dropped to the "0" state any time, but it must be dropped
at least O. 53 microseconds before another Input Data Request can be initiated. It should be noted that
the time relationships are such that the peripheral equipment desiring to send data at a maximum rate
could legitimately reset the Input Data Request before the previous Input Acknowledge has been dropped.
to the "O" state; however, the Input Acknowledge will always be returned to the "O" state before
being reset to the "1" state. This will not affect operation of the input cycle.
External Interrupt Inputs to Computer - Two different methods
2.2.1.2
are used to control the transmission of External Interrupts from peripheral equipment to the Computer.
Which method is used depends upon the peripheral equipment. If `the peripheral equipment is capable
of sensing an Interrupt Enable signal, then the control signals and timing are as shown in Method I of
Figure 1.3. If the peripheral equipment is not capable of sensing an Interrupt Enable, then the control
signals and timing are as shown in Method II of Figure 1.3. When Method I is used, the Interrupt
Enable line shall drop at the same time the Input Acknowledge is sent. This informs the peripheral
equipment that the computer has accepted the Interrupt word and that the Interrupt signal may be dropped.
Regardless of which method is used, a minimum delay of 3.75 (-O. 23) microseconds exist from
the start of the setting of the Interrupt Line, to the start of the setting of the Input Acknowledge line.
From the completion of the dropping of the Interrupt Line, a O. 53 microsecond minimum delay is
required before the start of the setting of the Interrupt line for the second time. The data lines must
remain stable as long as the Interrupt line is in the set condition.
Output Timing Considerations
2.2.2
Data Output and External Functions - Peripheral equipment
2.2.2.1
must first set the Output Request line or External Function Request line indicating that it is in a con-
dition to accept a data or External Function word from the computer. Data lines `will not necessarily
be cleared to the "O" state before being reset to the "1" state. The minimum time interval between
the Output or External Function Request signal and the placement of answering data on the lines is
6.75 (-O. 41) microseconds. The maximum time interval depends upon the computer program, the
priority of the particular channel, and the data request rates of the other peripheral equipment.
The Output Acknowledge or External Function signal indicates
to the peripheral equipment that the requested word is now present on the data lines and that the lines
should now be sampled. As shown in Figure 1-5, the Output Acknowledge or External Function signal
will be sent a minimum of 0.4 microsecond after the data has been placed on the lines. The periph-
eral equipment must be capable of recognizing, as an Output Acknowledge or an External Function, a
signal which may exist in the stable "1" state for as short a time as 2.2 microseconds. The computer
will maintain stable data on the lines for a minimum of 0.5 microsecond after it starts to drop the
Output Acknowledge or External Function.
332
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