C8051F340/1/2/3/4/5/6/7
Writing ‘1’ to INPRDY without writing any data to the endpoint FIFO will cause a zero-length packet to be
transmitted upon reception of the next IN token.
A Bulk or Interrupt pipe can be shut down (or Halted) by writing ‘1’ to the SDSTL bit (EINCSRL.4). While
SDSTL = ‘1’, hardware will respond to all IN requests with a STALL condition. Each time hardware gener-
ates a STALL condition, an interrupt will be generated and the STSTL bit (EINCSRL.5) set to ‘1’. The
STSTL bit must be reset to ‘0’ by firmware.
Hardware will automatically reset INPRDY to ‘0’ when a packet slot is open in the endpoint FIFO. Note that
if double buffering is enabled for the target endpoint, it is possible for firmware to load two packets into the
IN FIFO at a time. In this case, hardware will reset INPRDY to ‘0’ immediately after firmware loads the first
packet into the FIFO and sets INPRDY to ‘1’. An interrupt will not be generated in this case; an interrupt will
only be generated when a data packet is transmitted.
When firmware writes ‘1’ to the FCDT bit (EINCSRH.3), the data toggle for each IN packet will be toggled
continuously, regardless of the handshake received from the host. This feature is typically used by Inter-
rupt endpoints functioning as rate feedback communication for Isochronous endpoints. When FCDT = ‘0’,
the data toggle bit will only be toggled when an ACK is sent from the host in response to an IN packet.
16.12.2.Endpoints1-3 IN Isochronous Mode
When the ISO bit (EINCSRH.6) is set to ‘1’, the target endpoint operates in Isochronous (ISO) mode. Once
an endpoint has been configured for ISO IN mode, the host will send one IN token (data request) per
frame; the location of data within each frame may vary. Because of this, it is recommended that double
buffering be enabled for ISO IN endpoints.
Hardware will automatically reset INPRDY (EINCSRL.0) to ‘0’ when a packet slot is open in the endpoint
FIFO. Note that if double buffering is enabled for the target endpoint, it is possible for firmware to load two
packets into the IN FIFO at a time. In this case, hardware will reset INPRDY to ‘0’ immediately after firm-
ware loads the first packet into the FIFO and sets INPRDY to ‘1’. An interrupt will not be generated in this
case; an interrupt will only be generated when a data packet is transmitted.
If there is not a data packet ready in the endpoint FIFO when USB0 receives an IN token from the host,
USB0 will transmit a zero-length data packet and set the UNDRUN bit (EINCSRL.2) to ‘1’.
The ISO Update feature (see
) can be useful in starting a double buffered ISO IN endpoint. If
the host has already set up the ISO IN pipe (has begun transmitting IN tokens) when firmware writes the
first data packet to the endpoint FIFO, the next IN token may arrive and the first data packet sent before
firmware has written the second (double buffered) data packet to the FIFO. The ISO Update feature
ensures that any data packet written to the endpoint FIFO will not be transmitted during the current frame;
the packet will only be sent after a SOF signal has been received.
Rev. 1.0
189
SILABS [ SILICON LABORATORIES ]
