21020285 D User’s Guide
Chapter 2 Hardware Essentials
Page 2 - 10 Channel Attention Port
Determining a Control Field value - These are the significant points to
remember when determining the value you should use for the Control Field:
• The Control Field value is meant to be set once, usually during system
initialization. Generally, its value will be set with the first command
issued to the board.
• The values you choose for the Control Field will be applied immediately.
They will be applicable for the next parameter block read in and all fut ure
system memory accesses.
• The Control Field value is never applied to the Address Buffer Port or
any of the other hardware ports. Always follow the format given in this
section when accessing the hardware ports.
• Attempting to change the Control Field setting after the RF3880 adapt er
has begun executing a command list will cause unexpected results.
• The default value for the Control Field is zero; the adapter will operate
in 16-bit mode and the parameter and status block structures will not be
swapped.
Single Command Structure Address Fields
This two-word address is the starting address of the Single Command St ructure
containing the command to be issued to the board.
The Address Buffer Port is only used when issuing a Single Command to the
RF3880 adapter.
Channel Attention Port
The Channel Attention Port is a write-only port. It is used to direct the RF3880
adapter to execute Parameter Block(s) associated with a Command Structure
you have already built in system memory. The Channel Attention Port is used
for both Single and Command List issue. However, it is written slightly
differently in each case (as shown below).
Single Command Channel Attention - To initiate execution of a Single
Command you must do the following:
1. Construct a Single Command Structure in system memory.
2. Load the Address Buffer Port with the Control Byte, Address Modifier
and the address of the Single Command Structure constructed in Step 1.
3. Write a 0 to the Channel Attention Port, instructing the RF3880 adapter
to execute the Parameter Block contained in the Single Command
Structure.
Use an offset of 8H from your Base Address when writing to the
Channel Attention Port.