Synchronous Host Processor Interface - DDC Total-AceXtreme MIL-STD-1553 Design Manual

6.4

Synchronous Host Processor Interface

In Synchronous mode, the timing of transfers between the host CPU and the Total-
AceXtreme® is controlled by a clock provided by the host and connected to the
Total-AceXtreme's HOST_CLK input. The Total-AceXtreme can operate with
HOST_CLK speeds up to 80 MHz.
6.4.1 Types of Synchronous Mode Transfers
Within the Total-AceXtreme's Synchronous mode, there are three types of data
transfers that may be performed. These are:
• Single-word transfers.
• Sequential burst transfers.
• Random burst transfers.
Single-word transfers are limited to a single 32-bit transfer or a pair of 16-bit
transfers.
With both sequential and random Synchronous transfers, the host performs a series
of word transfers. In each case, during the active portion of the transfer, a 32-bit or
16-bit word is transferred during each cycle of the Total-AceXtreme's HOST_CLK
input.
With sequential burst transfers, the host CPU presents its starting address once, at
the beginning of the transfer. Following that, a transfer is performed between the host
and the starting address in the Total-AceXtreme's internal shared RAM. After that, a
series of transfers is performed between the host and successive address locations
in the Total-AceXtreme's internal shared RAM.
Random burst Synchronous transfers are not limited to transferring data to or from
successive locations in the Total-AceXtreme's internal memory. During the active
portion of a random Synchronous burst transfer, the host CPU presents a new
memory address during each cycle of HOST_CLK.
6.4.2 Operation of Command FIFO and CPU_nSTOP Signal
The Synchronous burst mode involves the use of a command FIFO within the Total-
AceXtreme. The size of the command FIFO is software programmable, with options
of 32, 16, or 8 words. The default size for the FIFO is 32 words.
There is one entry posted in the command FIFO for each 32-bit or 16-bit word to be
written to or read from the Total-AceXtreme. This includes the values of the Total-
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