Data Transfer Capabilities and Events Readout
The board features a Mul -Event digital memory per channel, configurable by the user to be divided into
1 up to 1024 buffers, as detailed in Sec.
. Once they are wri en in the
memory, the events become available for readout via USB or Op cal Link. During the memory readout,
the board can store other events (independently from the readout) on the available free buffers.
The events are read out sequen ally and completely, star ng from the Header of the first available event,
followed by the samples of the enabled channels (from 0 to 3) as reported in Fig.
. Once an event
is completed, the relevant memory buffer becomes free and ready to be wri en again (old data are lost).
A er the last word in an event, the first word (Header) of the subsequent event is readout. It is not possible
to read out an event par ally.
The size of an event (EVENT SIZE) is configurable and depends on register addresses 0x8020 and 0x800C
, as well as on the number of enabled channels.
Block Transfer
The Block Transfer readout mode allows to read N complete events sequen ally, where N is set at register
address 0xEF1C
, or by using the
SetMaxNumEventsBLT
func on of the CAENDigi zer library
.
When developing programs, the readout process can be implemented on different basis:
• Using
Interrupts
: as soon as the programmed number of events is available for readout, the board
sends an interrupt to the PC over the op cal communica on link
(not supported by USB)
.
• Using
Polling
(interrupts disabled): by performing periodic read accesses to a specific register of the
board it is possible to know the number of events present in the board and perform a BLT read of the
specific size to read them out.
• Using
Con nuous Read
(interrupts disabled): con nuous data read of the maximum allowed size (e.g.
total memory size) is performed by the so ware without polling the board. The actual size of the block
read is determined by the board that terminates the BLT access at the end of the data, according to
the configura on of register address 0xEF1C, or the library func on
SetMaxNumEventsBLT
men oned
above. If the board is empty, the BLT access is immediately terminated and the “Read Block” func on
will return 0 bytes (it is the
ReadData
func on in the CAENDigi zer Library
.
Independently from above method, it is suggested to ask the board for the maximum of events per block
being set. Furthermore, the greater this maximum, the greater the readout efficiency, despite a larger
memory alloca on required on the host sta on this is not a real drawback considering nowadays personal
computers.
Single Data Transfer
This mode allows the user to readout a word per me, from the header (actually 4 words) of the first
available event, followed by all the words un l the end of the event, then the second event is transferred.
The exact sequence of the transferred words is shown in Sec.
It is suggested, a er the 1st word is transferred, to check the EVENT SIZE informa on and then do as many
cycles as necessary (actually EVENT SIZE -1) in order to read completely the event.
46
UM3247 - N6724 User Manual rev. 10
