XR22804 Datasheet, PDF(12/47 Page) Exar Corporation – Hi-Speed USB to 10/100 Ethernet Bridge with 4 UARTs

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XR22804 Datasheet, PDF (12/47 Pages) Exar Corporation – Hi-Speed USB to 10/100 Ethernet Bridge with 4 UARTs

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XR22804

Table 2: Default XR22804 Product Strings

XR22804 Function

UARTs

I2C

EDGE

Default Product String

Exar USB UART

Exar USB I2C

Exar USB EDGE

The OTP may be used to override these strings. However, to ensure unique serial numbers for each device, it is recom-

mended that the factory pre-programmed serial number string be used and not be overwritten via OTP.

USB Device Drivers

Each of the functions in the XR22804 require a USB device driver for operation. Both the I2C and EDGE functions conform

to the HID device class and as such, utilize the embedded HID driver that is native to each Operating System. The embed-

ded hub also uses the native hub driver. The Ethernet function conforms to the CDC device class and as such can utilize an

embedded CDC-ECM driver. However, at the time of this writing, none of the Microsoft OS provide support for CDC-ECM

embedded drivers. Both Linux and Mac OS-X platforms do support CDC-ECM drivers.

The CDC-ECM is a "standard" driver which implements functionality on a specific class of devices. Exar provides a custom

Ethernet device driver for Windows operating systems which has been optimized for the best possible data through-put.

The UART function can be used with either a standard CDC-ACM driver or a custom driver. When the CDC-ACM driver is

used, the driver has no ability to read or write the XR22804 device registers. Because of this, the XR22804 device is initial-

ized to the settings in Table 3. With a custom driver, all GPIOs default in hardware to inputs but these settings may be mod-

ified by a custom driver.

Table 3: XR22804 Register Defaults With CDC-ACM Driver

Flow Control

GPIO_MODE

GPIO_DIRECTION

GPIO_INT_MASK

Value

0x001

0x008

0x030

Notes

Hardware Flow Control

RTS / CTS Flow Control

E3/DTRA#/GA3, E11/DTRB#/GB3, E19/DTRC#/GC3 and E27/

DTRD#/GD3 are configured as outputs. All other GPIOs as inputs.

E[n]/RI#/RWK#/G[n], E[n]/CD#/G[n] and E[n]/DSR#/G[n] for all

UART channels are interrupt sensitive, i.e. can cause a USB inter-

rupt to be generated

These default settings can be overridden by programming the OTP.

If a custom driver is used, the CUSTOM_DRIVER_ACTIVE bit should be immediately set to â1â by the USB UART driver.

Once the CUSTOM_DRIVER_ACTIVE bit is set, the custom driver can use standard CDC-ACM commands without config-

uring the device to the default register settings used with the CDC-ACM driver. Any changes to the register settings for the

GPIOs and flow control will specifically need to be configured by the driver / application software. Although there is no ability

to read / write registers when using the CDC-ACM driver, basic UART functions, including setting baud rate, character for-

mat and sending line break is supported by the CDC driver. Refer to the 4 CDC_ACM_IF USB Control Commands listed in

Table 4.

10/100 Ethernet

The Ethernet port is a 10/100 Ethernet MAC and Phy compliant with IEEE 802.3. The Ethernet port supports speed /

duplex auto-negotiation, auto-MDIX, 10 Mbps data auto-polarity, full and half duplex data rates at 10 and 100 Mbps, gener-

ates and validates the 32-bit FCS, and performs unicast and multicast filtering. The XR22804 also performs TCP, UDP and

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exar.com/XR22804

Rev 1B

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