How the IBM-Supplied Output Writer Routine Works

As stated previously, there are two main pieces to the external writer that can be modified or replaced by the installation: The output writer routine and the output separator routine. When the external writer is called, it gets control in module IASXWR00. The main function of IASXWR00 is to initialize a 7-word parameter list for the use of the other external writer routines.

The parameter list contains information about the output device and DCB addresses for each data set. The input data set to the external writer was a job's output data set which met the criteria for processing by the external writer. This input data set is not yet open.

The format of the external writer parameter list is as follows:

Table 1. External Writer Parameter List
Byte	Meaning
0	Used to describe the type of output device Bit Meaning 011. .... 2540 punch unit 001. .... 1403, 3203-5, 3211, or 3800 printer device 010. .... tape device with punch-destined output 000. .... tape device with printer-destined output
1-3	Reserved for IBM use
4-7	Address of the DCB for the opened output data set where the external writer will put the input records
8-11	Address of the DCB for the input data set, from which the external writer will obtain logical records.
12-15	Address of the cancel ECB for writer routine subtask (IEFSD087 or user-written writer routine).

The switches indicated by the three high-order bit settings in byte 0 can be used in translating control character information from the input records to the form required by the output device.