This is some information about my Canon LiDE 35. It is probably partly wrong.

GPIO-Infos:
name   function       dir startup scan
GPIO1: SCAN button    in  on      on
GPIO2: FILE button    in  on      on
GPIO3: E-MAIL button  in  on      on
GPIO4: COPY button    in  on      on
GPIO5: ?              in  on      on
GPIO6: ?              in  off     off
GPIO7: ?              in  off     on
GPIO8: ?              out off     on       
GPIO9: ?              out on      off
GPIO10: ?             out off     on
GPIO11: ?             out off     off
GPIO12: ?             out off     off
GPIO13: ?             in  on      on
GPIO14: ?             out off     off
GPIO15: ?             out off     off
GPIO16: ?             out off     off
GPO17: ?              out off     on       
GPO18: ?              out off     on
These are observations while playing with the GPIO pins:
- before switching GPIO17 from off to on GPIO8 must be on. GPIO8 can be reset 
  afterwards(Scanner hangs/reconnects? otherwise).
- GPIO16 is off during calibration. i get ff ff ff ... when off, 
  (like)45 12 41 ... when on
- if GPIO18 is off scanner does not stop at home position
- If GPIO9 is on the motor is switched off(not completely though. while 
  scanning it is still actuated, but not moving)
- if GPIO17 is off scanner does not light leds and does not detect "not home"

Motor: bipolar

Chips:
Genesys GeneScan III,GL842, USB 2.0 2-in-1 Scanner Controller
 GL842

Wolfson Microelectronics, WM8199CDS, 16bit 20MSPS Image Digitiser
 WM8199CDS

M11L41625SA, 3.3V EDO RAM 4MB(i didn't look inside mine, but should be similar)

motordriver chip: SANYO LB1940T
20pin : LB1940

other chips:
14pin :LA5664
SANYO LA5664M: "provides a stable 5V output for inputs from 4 to 5.6V"

14pin : 324
       Z27211/Z9S428
SGS-THOMSON Microelectronics(from Logo), Guess: LM324, Quad OpAmp

8 pin : 9953A(Dual P-Channel MOSFET?)/4801 
        A2288
no information about this one



FEEDL, SCANFED and LINECNT define steps
FMOVNO, STEPNO, FSHDEC, MOVDEC and DECSEL define pixel time (?)

FASTFED = 1
speed | FEEDL     |     
  ^    ---------->      | SCANFED | LINECNT       |
  !   ^           \      ------------------------->
  !  /             \    ^                          \
  ! /<--FMOVNO(4)-->\  /<--STEPNO(1)    FSHDEC(3)-->\
  !/                 v/                              v
--+---------------------------------------------------->position
  !^                                                 /
  ! \<--MOVDEC(5), DECSEL               FMOVNO(4)-->/
  !  \                                             /
  !   \                                           v
  !    <------------------------------------------

FASTFED = 0
speed      
  ^  | FEEDL      |                 LINECNT       |
  !   -------------------------------------------->
  !  ^                                             \
  ! /<--STEPNO(1)                       FSHDEC(3)-->\
  !/                                                 v
--+---------------------------------------------------->position
  !^                                                 /
  ! \<--MOVDEC(5), DECSEL               FMOVNO(4)-->/
  !  \                                             /
  !   \                                           v
  !    <------------------------------------------


speed 
  ^       buffer full v
  !------>------------>------------>
  !      ^             \
  !     /<--STEPNO(1)-->\
  !    /                 v
--+------------------------------->position
  !    ^                 /
  !     \<--FASTNO(2)-->/
  !      \             /
  !       \           v
  !        <----------

RAM:(1200dpi in hw)
+---------------+
!    0x00000    !red channel shading mapping
!    0x054ff    !
+---------------+
!    0x05500    !green channel shading mapping
!    0x0a9ff    !
+---------------+
!    0x0aa00    !blue channel shading mapping
!    0x0feff    !
+---------------+
!    0x10000    !slope curve table 1
!    0x101ff    !
+---------------+
!    0x10200    !slope curve table 2
!    0x103ff    !
+---------------+
!    0x10400    !slope curve table 3
!    0x105ff    !
+---------------+
!    0x10600    !slope curve table 4
!    0x107ff    !
+---------------+
!    0x10800    !slope curve table 5
!    0x109ff    !
+---------------+
!    0x10b00    !written to by windows driver
!    0x10cff    !
+---------------+
!    0x11000    !image data buffer
!0x3FFFF/0x7FFFF!
+---------------+

slope-tables:
little-endian 16bit.
each entry represents the pixeltime to wait before actuating the motor again
longest time(slowest) first. Two values per step.

white/dark-shading:
output=(input-darkvalue)*whitevalue/0x4000

gamma:
increment mode:
output is first value >= input
decrement mode:
output is last value <= input


gamma is calculated as usual. windows driver uses 2.2.

given a dark color dc and a bright color bc the white/darkvalue is:
whitevalue=0x40000000/(bc-dc)
darkvalue=dc

make sure to use the same settings for calibration and scanning, otherwise you 
may observe vertical lines.

There is an usb request which i cannot make sense of:
requesttype = REQUESTTYPE_IN
request     = REQUEST_REQISTER
value       = 0x8e
index       = 0x18 or 0x0c
results in one byte sent back
For index=0x18 result bit3 seems to indicate a bulk read/write in progress