AM3270/TR3271 Reference Manual

Details of the PRT Protocol
AM3270 Subdevice Protocols
086705 Tandem Computers Incorporated 4–19
CONTROL 1 Operation The CONTROL procedure is used by printer subdevices for forms control operations.
Line printer devices attached to a cluster controller may have forms operations
performed on them by application processes or Tandem subsystems. The PRT
protocol recognizes a CONTROL 1 call (VFU control) with a parameter set with one of
the following values:
param 0 skip to top of form
param 1-79 any number from 1 to 79, skip number of lines specified
(single space)
Forms operations cause the printer protocol to format an internal buffer with the
proper 3270 printer orders that represent the requested operation.
A printer subdevice must have a subdevice subtype of 0 (zero) for the above
operations to be allowed. A subtype other than zero causes the CONTROL operation
to be ignored (an error-free return occurs, but no action is performed).
WRITE Request A WRITE request results in a select operation being initiated for the subdevice. If the
select is accepted with no error received from the device, AM3270 adds the
communication control characters to the text to be written and writes it to the device.
Successful completion of the WRITE to the device causes the WRITE request to be
completed to the application process.
Error Handling The errors returned by AM3270 are the result of receiving either no response or an
improper response from the physical device. When the device indicates that status
information is available, status is solicited by AM3270 using a specific poll. Errors
returned to the application process are the result of a translation by AM3270 of the
actual status received by the device.