28 USB FUNCTION CONTROLLER (USB)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
28-21
DMAC trigger
PDREQ (O)
#PDREQ (O)
PDACK (I)
PDRD (I)
Data (O)
Data sampling
Inverted
D0
D1
Dn-1
Dn
5.3.3 Transfer Waveforms in Asynchronous Multi-Word DMA Transfer Mode - Reading
Figure 28.
Asynchronous single-word DMA transfer mode - slave
1) Writing operation
The Port interface starts writing operation in Asynchronous single-word DMA transfer mode when the fol-
lowing register settings are established:
• DMA_Config_1.SingleWord bit = 1
• Direction of the target endpoint = IN
The Port interface starts data transfer on the DMA when 1 is written on the DMA_Control.DMA_Go bit.
After data transfer starts on the DMA, the USB macro requests data transfer by asserting PDREQ if any
available space is found at the connected endpoint. The DMA loads the data and writes them to the end-
point when PDWR is rising (when the DMA_Config_0.PDRDWR_Level bit is set to 1). This mode negates
PDREQ after transferring 1-byte data (PDWR becomes active).
At this point, if any space is still available at the endpoint, it requests data transfer by asserting PDREQ. If
there is no available space left at the endpoint, PDREQ is not asserted and data transfer is rejected.
If any data is set to the DMA_Latency.DMA_Latency[3:0] bit other than 0x0, this mode negates PDREQ
once after completing transfer of 4-byte data, and does not assert PDREQ as long as 130 ns
×
N (N =
DMA_Latency.DMA_Latency[3:0]).
If the DMA is set to the Countdown mode with DMA_Config_1.CountMode = 1, the DMA completes data
transfer when the DMA_Count_HH, HL, LH and LL registers reach 0x00000000. To cancel (negate) the
DMA request (PDREQ), provide 1 to the DMA_Control.DMA_Stop bit. Note that writing 1 to the DMA_
Control.DMA_Stop bit does not stop the DMAC. So to terminate data transfer, first terminate the DMAC
(master) and then terminate the macro’s DMA transfer.
Note: The S1C33L26 DMAC can only be triggered to start data transfer by the Rising Edge of PDREQ.
The subsequent DMAC trigger will be issued at the next PDREQ Rising Edge. When the DMAC
transfer counter reaches 0, DMA transfer will not be started even if a DMAC trigger is issued.
Therefore, when using the USB macro in single-word DMA transfer mode, configure the DMAC in
single transfer mode and set the DMAC transfer counter to a value equal to or less than that set in
the DMA_Remain_H and DMA_Remain_L registers.
DMAC trigger
PDREQ (O)
#PDREQ (O)
PDACK (I)
PDWR (I)
Data (I)
Data sampling
Inverted
D0
D1
Dn-1
Dn
5.3.4 Transfer Waveforms in Asynchronous Single-Word DMA Transfer Mode - Writing
Figure 28.