Silicon Laboratories Stepper Machine Specifications download pdf (Page 16)

USB Transfers—Closer Look at Bulk/Interrupt Transfers

 Bulk and interrupt transfers

 Contains IN/OUT, Data, and handshake transactions

 Bulk schedules transfers as bus bandwidth permits

 Interrupt schedules transfers on regular intervals. Data may be delivered at a faster rate than the

endpoint descriptor value.

PID=1001

DATA

PID=1011

ACK

PID=0010

NAK

PID=1010

STALL

PID=1110

OUT

PID=0001

DATA

PID=0011

ACK

PID=0010

NAK

PID=1010

STALL

PID=1110

Data IN Transaction

Data OUT Transaction

Data error

Data Size:

Bulk: 8, 16, 32, or 64 bytes

Interrupt: 1 to 64 bytes FS

1 to 8 bytes LS

Host sends IN packet and the device responds with the

data requested. Host responds with handshake. No

response indicates a data error.

Host sends OUT packet and then continues with the data.

Device responds with handshake. No response indicates

a data error.

Data transfer continues until the complete length of

data has been sent or a packet less than the minimum is

sent with a 0-length data packet.

Host → Device

Device → Host

All of the transfer types follow the same convention as the control transfer with the

exception that they differ in the number of transactions that are required to complete

the transfer. The Bulk and Interrupt transfers each have the same format and are

denoted by the IN and OUT PIDs. These transfer types use what is called the

MAX_PACKET_SIZE parameter (which is a USB parameter defined by in the USB

peripheral) to transfer the data. All data transactions must transfer the data in

multiples of the maximum packet size. If a packet less than the maximum number

of bytes is sent then it tells the host that there is not more data. If the data being

transferred is an even multiple of the MAX_PACKET_SIZE parameter then an

additional Data transaction needs to added with a Zero Length Packet (ZLP).

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Silicon Laboratories Stepper Machine Specifications Page 16

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