BitFlow NEO-PCE-CLB, Hardware Reference Manual

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The Control Tables (CTABs) The Neon
NEO-2-18 BitFlow, Inc. Version G.5
The “Stop at Zero” Case
Usually, HCOUNT will reach zero because of a RESET_H signal. After HCOUNT is
reset, there are two programmable options:
HCOUNT keeps on counting.
HCOUNT stays at zero until ENCODER is asserted.
The selection between the two options is done by the HCNT_RLS_ZERO bitfield, see
next section on camera synchronization.
This operating mode is especially useful for synchronizing line scan cameras to exter-
nal events. ENCODER is usually the output of an encoder or a tachometer signal. Until
this signal is asserted, the HCOUNT waits at address 0000h. After the ENCODER is
asserted, HCOUNT starts counting, i.e., scanning the HCTAB in ascending order. At
some address we will program a sync signal to be sent to the scan camera, usually
through GPH0. In response to this sync signal, the camera will give back a line, and it
will assert LEN. The LEN will load address 2000h into HCOUNT. In the HCTAB, we will
program the horizontal acquisition window after address 2000h. At the end of the
horizontal acquisition window the RESET_H will be asserted, which in turn will reset
the HCOUNT. HCOUNT will wait at address 0000h until ENCODER is asserted.
Horizontal Stick
Using the previous example, assume that after we asserted the sync signal to the cam-
era, we expect the camera to give us a line, i.e., assert LEN. While we expect the cam-
era to assert LEN, HCOUNT is still being incremented. If it takes too long for the
camera to respond, HCOUNT will eventually reach and pass beyond 2000h. A hori-
zontal acquisition window will be asserted even though the camera did not assert
LEN. To avoid such a situation, just before address 2000h, when HCOUNT reaches
1FF0h, it will stop. It will stay at 1FF0h until LEN is asserted. Then, HCOUNT will be
loaded with 2000h.
The LOAD_H Control
LOAD_H is the logic of loading HCOUNT.
HCOUNT will be loaded with the value 2000h by the rising/falling edge of LEN, if
ENHLOAD is asserted. LEN usually marks the start of valid data in a line. The Horizon-
tal Acquisition Window can be placed starting at address 2000h.
ENHLOAD is a column in the HCTAB that enables the LEN. There are cameras that do
not assert LEN. In that case, the LEN input must be disabled, otherwise its behavior is
unpredictable.
Operation on the rising/falling edge of LEN is selected by LENPOL, see CON14.
The RESET_H Control
RESET_H is the logic of reset HCOUNT.
HCOUNT can be reset from several sources, according to HCNT_RST bitfield, see next
section on camera synchronization.