Light Pen Mode Orders - IBM 2250 3 Manual

Upon execution of the Store X-Y Deflection
Registers in Buffer order, buffer regeneration
continues from location N + 4.
Move Immediate Address (GMVA)
N, N+l
2A
EB
N+2, N+3 Specifies address in which to store N+4, N+5
N+4, N+5 Buffer address to be stored
0 1 2 7 8
14 15
This six-byte order enables an address located in
the buffer program to be relocated to another portion
of the buffer.
The address stored in locations N + 2 and N + 3
specifies the buffer location at which the address
stored in locations N + 4 and N + 5 is to be inserted.
Note that bit 15 of the address specified in N + 2 and
N + 3 is not checked; therefore, an even address is
always selected, regardless of whether bit 15 is a
0 or a 1. Alter execution of this order, the next
order for the 2250 receiving service will be taken
from address N + 6. If location N + 4 contains an
SM byte, the SM byte will be treated as part of an
address, not as an order during execution of the
Move Immediate Address order.
Move Immediate Data (GMVD)
This order is identical in format (except for the MC
code, which is EC) and execution with the Move
Immediate Address order. However, locations N + 4
and N + 5 normally contain data instead of an address.
Light Pen Mode Orders
2A 83
0
7 8
15
Light pen mode orders are used primarily for graphic
design operations.
Defer Response to Light Pen Detects (GDRD)
This order is executed for a 2250 only when an
Enable Switch Detect Operation order or an Enable
No Switch Detect Operation order is active for the
2250. Following the decoding of a Defer Response
to Light Pen Detects order, the occurrence of one
or more light-pen detects at the 2250 is remembered
as associated with that 2250.
The remembered, or "pending" , detect condition
is held until any one of three orders is encountered
in the buffer program for the 2250. These orders
and the actions they cause when a detect condition
is pending are as follows:
1. Transfer on Deferred Detect - Regeneration
for the 2250 continues from the buffer address
specified in this order.
2. Transfer on No Detect - This order causes no
operation.
3. Permit Detect Interrupts - Generates a light-
pen interrupt to the channel.
The two transfer orders reset the pending detect
condition and permit a new deferred detect condition
to occur. The deferred response mode established
by the Defer Response to Light Pen Detects order
is reset only by a Permit Detect Interrupts order
or by a Start Regeneration Timer order.
Enable Switch Detect Operation (GESD)
2A
84
0
7 8 15
This order causes the 2250 to operate in the normal
Light Pen Detect mode. Each detect is controlled
by the light-pen switch and is synchronized with the
Start Regeneration Timer order.
Two orders cause the 2250 to leave the normal
Detect mode: Enable No Switch Detect Operation,
and Disable Light Pen Detects. The 2250 is reset
to normal Detect mode either by an Enable Switch
Detect Operation .order or by a Start Regeneration
Timer order. In normal Detect mode, the sequence
of conditions that results in a detect is as follows:
1. The light-pen switch is closed.
2. A Start Regeneration Timer order is
encountered following switch closure.
3. The 2250 is in normal Detect mode at the
time displayed information is viewed by the
light pen (i.e., at the time the information
is displayed for detection) .
Since light-pen detection depends on this sequence of
events, a detect will occur on the first character,
point, or vector that is displayed within the light-pen
field of view following execution of the Start Regener-
ation Timer order; thus , a hierarchy of detects can
be established by the programmer.
Only one normal light-pen detect can occur for
each switch closure.
If a normal detect occurs, and if the 2250 is not
in the Defer Response to Light Pen Detects mode, a
light-pen interrupt is presented to the channel when
the 2840 status and sense registers are available,
and regeneration for the 2250 stops immediately. If
the 2250 is also in the Defer Response to Light Pen
Detects mode and a normal light pen detect occurs ,
regeneration for the 2250 continues , a light-pen
2840 Operations with Attached 2250's 23