Channel commands for channel-to-channel (CTC) adapters
Table 1 contains the channel commands used for channel programs between two hosts connected by a channel-to-channel adapter.
| Command |
|
|
|---|---|---|
| 01 | Write | Transfers data from storage in this host processor to the CTC
adapter (CTCA). For CTCAs, this CCW is used to transfer status information
from XCNOCTL, XID information from PIOPOTXT, validity checking information
from XCNOVTXT, and data from buffers. Status information, mapped by XCNOCTL, is transferred in the first 8 bytes of the write buffer, and only one write buffer is used. Figure 1 illustrates the buffer usage. For MPC connections this CCW, preceded by a Prepare command, is used to transfer data from the CPNCB transmit buffer. The transmit buffer is defined by YCNOBUF of the YCNCB contained within the CPNCB. The first 8 bytes of the transmit buffer is mapped by ISTBKHDR and contains control information about the current data transfer. Figure 1 illustrates the MPC buffers used for normal data transfer. |
| 02 | Read | Transfers data from the CTCA to this host processor. For CTCAs,
this CCW is used to read status information into XCNICTL, XID information
into PIOPITXT, validity checking information into XCNIVTXT, and data
into buffers. Status information, mapped by XCNICTL, is transferred in the first 8 bytes of the read buffer, and only one read buffer is used. Figure 1 illustrates the buffer usage. For MPC, this CCW is used to read normal data into the CPNCB transmit buffer. The transmit buffer is defined by YCNIBUF of the YCNCB contained in the CPNCB. Figure 1 illustrates the MPC buffers used for normal data transfer. |
| 03 | No-Op | Causes the channel to respond with a channel end or device
end. It is the last CCW in a read or write chain. The No-Op command does not apply to the MPC connection. |
| 08 | TIC | Causes the channel program to execute an instruction that is
not the next sequential instruction within the channel program sequence.
The TIC command does not apply to the MPC connection. |
| 14 | Sense Command Byte (SCB) | The SCB is normally issued in response to an attention generated when the adapter processes a WCTL from the other side. The SCB clears WCTL from the adapter, allowing the WCTL CCW to complete. |
| 17 | Write Control (WCTL) | Causes an attention interruption on the other side of the channel-to-channel adapter. The WCTL is issued to alert the other side that a channel program is active at the adapter. |
| 43 | Enable Compatibility Mode (ECM) | Prepares the adapter to operate in System/360 (compatibility) mode. The ECM is issued when VTAM® gives up control of the adapter. |
| C3 | Disable Compatibility Mode (DCM) | Prepares the adapter to operate in System/370 (extended) mode. The DCM is issued when VTAM acquires control of the adapter. |
| E3 | Prepare | Primes the CTC adapter for the next CCW. This CCW does not
cause an attention on the other side of the adapter. The Prepare command applies only to the MPC connection. |