My investigation of the CanoScan 8400F has so far found the following.
cat /proc/bus/usb/devices : ... T: Bus=01 Lev=01 Prnt=01 Port=05 Cnt=01 Dev#= 29 Spd=480 MxCh= 0 D: Ver= 2.00 Cls=ff(vend.) Sub=ff Prot=ff MxPS=64 #Cfgs= 1 P: Vendor=04a9 ProdID=221e Rev= 4.00 S: Manufacturer=Canon S: Product=CanoScan C:* #Ifs= 1 Cfg#= 1 Atr=c0 MxPwr= 10mA I: If#= 0 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=ff Prot=ff Driver=(none) E: Ad=81(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms E: Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms E: Ad=83(I) Atr=03(Int.) MxPS= 1 Ivl=16ms sane-find-scanner output: ... <device descriptor of 0x04a9/0x221e at 001:029 (Canon CanoScan)> bLength 18 bDescriptorType 1 bcdUSB 2.00 bDeviceClass 255 bDeviceSubClass 255 bDeviceProtocol 255 bMaxPacketSize0 64 idVendor 0x04A9 idProduct 0x221E bcdDevice 4.00 iManufacturer 1 (Canon) iProduct 2 (CanoScan) iSerialNumber 0 () bNumConfigurations 1 <configuration 0> bLength 9 bDescriptorType 2 wTotalLength 39 bNumInterfaces 1 bConfigurationValue 1 iConfiguration 0 () bmAttributes 192 (Self-powered) MaxPower 10 mA <interface 0> <altsetting 0> bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 3 bInterfaceClass 255 bInterfaceSubClass 255 bInterfaceProtocol 255 iInterface 0 () <endpoint 0> bLength 7 bDescriptorType 5 bEndpointAddress 0x81 (in 0x01) bmAttributes 2 (bulk) wMaxPacketSize 512 bInterval 0 ms bRefresh 0 bSynchAddress 0 <endpoint 1> bLength 7 bDescriptorType 5 bEndpointAddress 0x02 (out 0x02) bmAttributes 2 (bulk) wMaxPacketSize 512 bInterval 0 ms bRefresh 0 bSynchAddress 0 <endpoint 2> bLength 7 bDescriptorType 5 bEndpointAddress 0x83 (in 0x03) bmAttributes 3 (interrupt) wMaxPacketSize 1 bInterval 8 ms bRefresh 0 bSynchAddress 0 <trying to find out which USB chip is used> ... checking for GL646 ... this is not a GL646 (bDeviceClass = 255, bInterfaceClass = 255) checking for GL646_HP ... this is not a GL646_HP (bcdUSB = 0x200) checking for GL660+GL646 ... this is not a GL660+GL646 (bDeviceClass = 255, bInterfaceClass = 255) checking for GL841 ... <This USB chip looks like a GL841> found USB scanner (vendor=0x04a9 [Canon], product=0x221e [CanoScan], chip=GL841) at libusb:001:029 ... Brian JD