USB97C201 datasheet(43/59 Pages) SMSC

43 / 59 page

SMSC USB97C201

Page 43

Rev. 11-05-03

DATASHEET

6.2.1

AUTONOMOUS USB PROTOCOL

6.2.1.1

Automatic Retries - Out Transactions

If a packet is received with an incorrect data toggle, the SIE will ACK, but ignores the data packet. If more than 64

bytes received on EP0RX or EP1RX, or if more than 512 bytes are received on EP2, the USB SIE will ignore the

packet and set the appropriate “STALL” bit until the host acknowledges the condition by sending a “CLEAR

FEATURE ENDPOINT STALL” command for that endpoint, or, in the case of Endpoint 0, a SETUP is recieved.

If an error occurs during an OUT transaction, the USB97C201 reloads its USB SIE read pointer back to the beginning

of the buffer. The host then sends another OUT token and retransmits the packet.

Once the packet has been successfully received, the appropriate interrupt bit is set in ISR_0 or ISR_1. The SIE can

handle any number of back-to-back retries, but the host determines how many times a packet is retried.

If an endpoints’s buffer or buffers (in the case of EP2) are full, then the SIE sends a NACK. A TX direction Endpoint

will NAK all OUT packets.

6.2.1.2

Automatic Retries - In Transactions

If an timeout (No response from the host / lost ACK) occurs during an IN transaction, the USB97C201 reloads its USB

SIE side buffer read pointer back to the beginning of the failed packet. The host then sends another IN token and the

SIE re-transmits the packet with the same data toggle PID.

Once the host has successfully received the packet (only upon ACK received by SIE), the appropriate interrupt bit is

set in ISR_0 or ISR_1. The SIE can handle any number of back-to-back retries, but the host determines how many

times a packet is retried.

Upon reception of a SETUP token followed by the 8 byte DATA-0 packet on EP0, the internal DTOG bit for both

EP0RX and EP0TX are set to one.

6.2.1.3

Packet Lengths

The maximum packet length of an endpoint is fixed and 64 bytes for EP0 and EP1, and is 512 bytes for EP2 in HS

mode and 64 bytes in FS mode. For IN transactions, the USB97C201 will send the bytes in the buffer to the host. For

all OUT packets, the number of bytes received in the packet is indicated to the 8051 through the

BYTE COUNT

6.2.2

USB EVENTS

There are several events, which cause different parts of the SIE to be initialized. The following is the list of events and

the respective actions.

6.2.2.1

Reset

A reset via the external nRESET pin causes the following:

All endpoints are disabled, all SIE endpoint buffers are cleared, all stall conditions, and all registers clear to their

default state.

If USB97C201 was in power down state, then it is cleared.

The external crystal oscillator is allowed to run.

6.2.2.2

USB Bus Reset

USB Bus Reset is recognized only when the clocks are running. If the device is in SUSPEND mode with the clocks

stopped, a USB RESET will be first recognized as a RESUME event and if the WU_SRC1 bit for RESUME is

unmasked, will restart the clocks. The USB RESET can only then be detected. Upon recognition it causes the

following:

All SIE endpoint buffer byte count registers are cleared, all stall conditions, the SETUP bit, SETUP_DELAY bit,

SIE_SUSPEND, SIE_RESUME are cleared. The PID sequencers, internal DTOG are reset for all endpoints

The following registers will be set to their POR values: USB_ADD, SIE_STAT, USB_CONF, EP0RX_CTL,

EP0TX_CTL, EP1RX_CTL, EXP1TX_CTL, EP2_CTL, EP0RX_BC, EP0TX_BC, EP1RX_BC, EP1TX_BC,

RAMWRBC_A1,

RAMWRBC_A2,

RAMWRBC_B1,

RAMWRBC_B2,

RAMRDBC_A1,

RAMRDBC_A2,

RAMRDBC_B1, RAMRDBC_B2, NAK, USB_ERR.

The seven bit USB device address is cleared.

Both EP0TX and EP0RX endpoints are enabled.

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