
Applied Micro Circuits Corporation
6195 Lusk Blvd., San Diego, CA 92121 (619) 450-9333
15-28
ADD-ON DMA CONTROLLER DESIGN FOR THE S5933
2.1.2
Transfer Count Register (TXCNT)
The transfer count register contains the current number of bytes left to be transferred. Before the DMA transfer
begins, the TXCNT register is written with the total number of bytes to be transferred. All transfers counts must
be multiples of 4 bytes. The TXCNT register is decremented by 4 bytes after each data phase completes. Bit 24
of the TXCNT register controls the direction of the DMA transfer (read from the S5933 or write to the S5933).
Register Name:
DMA Byte Transfer Count (TXCNT)
Location:
A21=1, A20=1
Power-up Value:
00000000h
Attribute:
Write Only
Size:
32-bits
2.2
DMA Controller Bus Interface
The DMA controller bus cycles are identical to bus cycles performed by an Intel 80960Jx processor. This allows
the DMA controller to transfer data to and from any peripheral or memory controller compatible with the i960Jx
processor. The PLD state machines can easily be modified to emulate other processor bus cycles.
The following signals make up the bus interface for the DMA controller:
Signal
Type
Function
A31:0
Bidirectional
Address/data lines for accessing DMA registers.
RDY_IN#
Input
Ready Input for DMA controller-generated bus cycles.
RDY_OUT#
Output
Ready Output for processor-generated bus cycles.
BLAST#
3-State
Indicates that the current data phase is the last data phase of a burst.
ADS#
Bidirectional
Indicates that valid address information is currently on the bus.
W/R#
Bidirectional
Write/Read indicator.
BE3:0#
3-State
Byte Enables. Always asserted for DMA transfers.
RDFIFO#
Output
Read one double-word from the S5933 FIFO.
WRFIFO#
Output
Write one double-word to the S5933 FIFO.
HOLD
Output
Add-on processor hold request.
HLDA
Input
Add-on processor hold acknowledge.
RESET#
Input
Add-on reset signal (from the S5933)
All bidirectional signals are driven by the current add-on bus master. When the add-on processor controls the
bus, the DMA controller floats these outputs.