Full Screen Interactions
CCW code X'2A' performs a READ BUFFER or a READ MODIFIED operation,
depending on the value of the control field.
To specify the full screen mode CCW, use the following assembler language
instructions: DS OD DC AL1 (CCWCODE),AL3(DATADDR) ,AL1(FLAGS) ,AL1 (CONTROL) ,AL2(COUNT) where: CCWCODE is a CCW code (X'29' or X'2A')
DAT ADDR for a write operation, specifies the first byte of the data stream
(WCC) to be written. For a read operation, specifies the address of
the read buffer.
FLAGS is the standard CCW flag field. CONTROL for a write operation, an ERASE/WRITE is performed by specifying
a ccwcode of X'29', if the high-order bit (X'80') is on. If the two
high-order bits (X'CO') are on, an ERASE/WRITE ALTERNATE is
performed. If bit 2 (X'20') is on, a WRITE STRUCTURED FIELD
is performed. COUNT If the high-order bit (X'80') is on for a read operation, a READ MODIFIED is performed; otherwise, a READ BUFFER is performed.
The addition of X' 10' to the CONTROL field values for
ERASE/WRITE or ERASE/WRITE ALTERNATE, making them X'90' or X'DO' respectively, causes the PAl key interrupt to be
reflected to the virtual machine. This replaces the normal PAl key
function of returning the virtual machine to CP mode. This allows a
virtual machine to have full control of the keyboard. Normal PAl key
function is restored when full screen mode is reset.
for a write operation, specifies the number of bytes to be displayed
plus the number of bytes of control information. For a read operation,
specifies the number of display characters to be read plus the number
of bytes of control information. The maximum number of bytes that
can be specified is 65503. The maximum number of displayable posi­
tions for the supported devices is:
3277 and 3275 Model 2 - 1920 bytes
3278,3276 and 3279 Model 2 - 1920 bytes
3278, 3276 and 3279 Model 3 - 2560 bytes
3278 and 3276 Model 4 - 3440 bytes
3278 ModelS -3564 bytes
The virtual machine console exists in either of two modes, CP mode and full screen
mode. CP mode is the default screen mode and is indicated by the screen status
field in the lower right-hand corner of the screen. When in CP mode, the screen
format is controlled by CP, and the data that appears on the screen is provided by
CP and the programs running in the virtual machine. Full screen mode is initiated DIAGNOSE Instruction in a Virtual Machine 249

by the application program running in the virtual machine. When in full screen
mode, the screen format and data are under complete control of the program run­
ning in the virtual machine.
If TERMINAL BREAKIN GUESTCTL is specified, the screen mode changes only
when the break-in key is used. An audible alarm is sounded when CP messages are
queued. Priority CP messages and DIAGNOSE X'08' output take over the full
screen. CP mode is terminated and full screen mode is initiated when the application pro­
gram issues an ERASE/WRITE instruction. Full screen mode may be terminated
by a CP mode type I/O to the screen any time the keyboard is in a locked state.
Interactions between CP and the application program in the virtual machine using
full screen support are listed below. The application programmer must be familiar
with the operation of the IBM 3270 display station. For detailed information on its
operation, see the appropriate 3270 Information Display System Description and
Programmer's Guide listed in the Preface. Also listed below are general program­
ming considerations that must be followed to effectively use the DIAGNOSE X'58'
instruction for full screen I/O. 1. A full screen ERASE/WRITE or ERASE/WRITE ALTERNATE operation
establishes full screen mode.
2. The application program is responsible for all I/O status and error checking,
just as if START I/O (SIO) were being used instead of DIAGNOSE. This is
done by using the TEST I/O (TIO) instruction and examining the returned
condition code, and by examining the virtual CSW. The returned condition
codes and CSW status are the standard condition codes and status as defined
in the IBM System/3 70 Principles of Operation, with one exception noted
below in number 5.
3. When in full screen mode, all CP messages are queued. The entire queue of CP messages is processed after each of the following operations:
a. A full screen READ operation (any READ operation that locks the key­
board).
b. A full screen WRITE operation that does not place the keyboard in the
active status.
c. The expiration of a 60 second timer for CP priority messages.
4. If a priority CP message (such as a warning message from the system operator)
is to be displayed while in full screen mode, an attention interruption is posted
to the application program and a 60 second timer is set. This informs the
application program that a READ operation should be initiated. If a READ is
not issued before the 60 seconds have expired, CP erases the screen and dis­
plays all queued messages.
The only exception is if the application program has issued a Full Screen Sup­
port WRITE STRUCTURED FIELD instruction. CP does not take over the
screen if the user has issued a WRITE STRUCTURED FIELD.
5. When a mode switch has occurred and the screen is in CP mode, the applica­
tion program is notified by an X'8E' in the CSW unit status byte following a 250 VM/SP System Programmer's Guide