Protocol analysis
R&S
®
RTE
820User Manual 1326.1032.02 ─ 20
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EOP (end of package): the devices determine the length of the data field with the
EOP signal, which indicates the end of a packet. In low and full speed, it consists
of two SE0 bits, followed by a J state. For high speed, the current state is inverted
and kept for 7-bit times, leading to a Bitstuff error that is used as an EOP indicator.
This corresponds to the bit sequence 01111111 ahead of NRZI; for the SOF token,
the bit sequence 0111111111111111111111111111111111111111 is transmitted (five
NRZI bytes), which is used to recognize disconnects (since high-speed devices
normally do not apply voltage to D+/D-). If no device is present, a higher voltage is
measured. After that, the idle state (SE0) is occupied.
Table 13-22: Valid PIDs for different packet types
Packet
type
Name PID
value
Meaning
Token OUT 0xE1 Starts data transfer towards a device
IN 0x69 Starts data transfer towards the host
SOF 0xA5 Indicates start of frame
SETUP 0x2D Starts a setup transfer and sends information on this to the device
Data DATA0 0xC3 Data packet with data-toggle bit 0
DATA1 0x4B Data packet with data-toggle bit 1
DATA2 0x87 Data packet for high speed IN isochronous transfers that require high
bandwidth
MDATA 0x0F Data packet for high-speed OUT isochronous transfers that require
high bandwidth
Handshake ACK 0xD2 Acknowledgement of a packet received without error
NAK 0x5A Data not accepted, typically equivalent with some type of EAGAIN,
meaning that the data should be resent later
STALL 0x1E A severe error has occurred, the target endpoint cannot be addressed
until it is explicitly cleared again
NYET 0x96 Only used in high-speed transfers, meaning ACK, but in the next inter-
val no data can be received, therefore the host should first apply a
PING
Special PRE 0x3C Starts a low speed transfer via a full speed bus
ERR 0x3C Indicates an error in an SPLIT transaction (using the same PID as
PRE, however, these cannot be mistaken for each other)
SPLIT 0x78 Starts an SPLIT transaction (thus: a low speed or full speed transfer
via a high-speed bus)
PING 0xB4 Used for monitoring high-speed data flow
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Token packets (IN, OUT, SETUP) and PING packets have the following format:
SYNC PID ADDR ENDP CRC5 EOP
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Start of frame packets (SOF) have the following format:
USB (option R&S
RTE-K60)
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