28 USB FUNCTION CONTROLLER (USB)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
28-59
D7
RcvLimitMode
Setting this bit to 1 realizes the RcvLimit mode. This function is available only during write operation
for the asynchronous multi-word DMA transfer, and not available in the count down mode.
During the asynchronous DMA write operation in the RcvLimit mode, data up to 16 bytes can be re-
ceived even after this macro negates the PDREQ signal.
In this mode, the PDREQ signal is negated when the space of the endpoint becomes less than 32 bytes
by the DMA write operation. However, when the PDREQ signal is negated, 16-byte data that are not
written into the endpoint may exist in the internal circuit. Therefore, the data that can be received after
the PDREQ signal is negated, is 16 bytes or less.
In this mode, the PDREQ signal is negated before the endpoint becomes completely full.
When the area of the endpoint set by the EP{a,b,c,d}StartAdrs registers is the same as the value set by
the EP{a,b,c,d}MaxSize register (Single Buffer), the endpoint never becomes full. Therefore, the data
cannot be transmitted by the IN transfer of the USB.
To avoid this limitation, when using the RcvLimit mode, be sure to enter the value of the EP{a,b,c,d}
MaxSize re 32-byte or larger area, into the EP{a,b,c,d}StartAdrs register.
Note: In the S1C33L26, the USB DMA data transfer count is determined according to the DMAC
transfer counter setting. Negating PDREQ by the USB macro does not affect the transfer
count. So in RcvLimit mode, the DMAC continues data transfer until the DMAC transfer coun-
ter reaches 0 even after the macro negates PDREQ. Therefore, make sure that the DMAC
transfer counter is set properly.
D[6:4]
Reserved
D3
SingleWord
Sets the handshake mode in the Asynchronous (handshake) mode.
In the Single Word mode, the PDREQ signal is negated every time when one word is transferred.
In the Multi-Word mode, the PDREQ signal is not negated if the next data communication is possible
when one word is transferred.
Notes: • In multi-word DMA transfer mode, the DMAC can only be triggered to start data transfer by
the Rising Edge of PDREQ. After that no DMAC trigger will be issued while PDREQ stays
active (high level). The subsequent DMAC trigger will be issued at the next PDREQ Rising
Edge. Therefore, when using the USB macro in multi-word DMA transfer mode, configure
the DMAC in successive transfer mode and set the DMAC transfer counter to the same
value set in the DMA_Remain_H and DMA_Remain_L registers.
• In single-word DMA transfer mode, the 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.
D[2:1]
Reserved
D0
CountMode
Sets the mode to control the number of the DMA transmissions.
In the free-run mode, the DMA transfer operation is continued until the DMAC is stopped. The Trans-
fer Byte Counter (DMA_Count_HH, HL, LH, LL) shows the number of transmissions for reference.
In the Count-down mode, the DMA request (PDREQ) signal is asserted up to the number of bytes set in
the Transfer Byte Counter (DMA_Count_HH, HL, LH, LL) or until the DMA_Stop is enabled to stop
it. The Transfer Byte Counter shows the remained transmission quantity, for reference.