Control Messages

Control messages perform functions, such as starting the LAN and obtaining the hardware addresses of the LAN adapters. Figure 1 shows the structure of a PCCA control message, which has three fields.

The following are descriptions of the fields shown in Figure 1.
  • Net Type (1 byte); X'00' for control messages

    This field helps to determine whether the packet is used for control or LAN operations.

  • Adapter Number (1 byte); X'00', ignored for control messages
  • Control field
    • Control command (1 byte)
      • X'00' Control Timing (sent by PCCA)
      • X'01' Start LAN
      • X'02' Stop LAN
      • X'04' LAN Stats
      • X'08' Shutdown
    • Control flags (1 byte)
      • X'00' From host
      • X'01' From PCCA
    • Control sequence (1 halfword)
    • Return code (1 halfword)
    • Net type_2 (1 byte)

      This is the net type of the adapter referred to by the control packet.

    • Adapter number_2 (1 byte)

      This is the number of the adapter referred to by the control packet.

    • Count (1 halfword)

      This occurs at startup. It is used for block size or a count of items in the data field (general control packet has 56 bytes, X'38').

    • Control reserved
    • Ignored (1 halfword)
    • Hardware address (6 bytes).
Figure 1. PCCA Control Message Structure

+------+------+------------------------+
| X'00'| X'00'| Control information    |
+------+------+------------------------+