Rainbow Electronics AT77C104B - Manual (Page 26)

26
AT77C104B
5347B–BIOM–08/04
Figure 16. Reading of Frame
Notes: 1. For the first array or frame reading, 40 dummy clock cycles must be sent before the first data arrives. This is necessary for
the initialization of the chip pipeline. Consequently, the first synchronization sequences appear after 40 clock cycles. For the
following array readings, data arrives at each clock cycle. One should implement a synchronization routine in the protocol to
look for the F0F00200 pattern.
2. The Most Significant Bit (MSB) is sent first.
Reading of Entire Image The FingerChip delivers fingerprint slices or frames with a height of 0.4 mm and a width
of 11.6 mm (this equals 8 × 232 pixels). Pixels are sampled/read sequentially and are
synchronous with SCK. Raw slices are captured by the acquisition system and over-
lapped with the corresponding X or Y finger displacement computed by Atmel
reconstruction software. This reconstruction software supports a sweeping speed from 2
to 20 cm/s.
The table below shows finger speeds according to the different clock frequencies. The
reconstruction results are obtained after acquisition of all slices.
SCK
MISO
Dummy Column
F 0 F 0 2 0 0 P2 P1 P4 P6 P3 P5 P8 P7
First Pixel
Column
0 P10 P9
Second Pixel
Column
Table 14. Finger Speeds Versus Clock Frequencies
Fsck
(MHz) Data Rate
(Mbit/s) Slice Rate
(Slices/s)
Absolute
Maximum Finger
Speed (cm/s)
Comments
1 1 134 3 Too slow
2 2 268 6 Too slow
4 4 536 12 Minimum
6 6 804 18 Normal speed
8 8 1072 24 Good speed
12 12 1608 36 Very good speed
16 16 2146 48 Very good speed