13.2.1 Validate
The input can used as a Validate control to reduce the amount of data read out of the chip. The
input is used to make a hit valid for readout. The VAL input must be high at the point where the data
is saved in a channel for it to be written into the data buffer. If the input is low when this occurs then
no data will be written into the data buffer and therefore no data will be read off chip for that
particular hit. The channel will continue to process the data, and reset itself as usual, it is just not
stored in the data buffer to be read out. In a second mode it can be set permanently high.
13.2.2 Calibrate
The input can be used as Calibrate control. A pulse applied on this input will generate an analogue
calibrate pulse to any channel selected for calibration.
13.2.3 Timestamp reset
The input can be used to reset the timestamp counter, thus synchronising the timestamps of all
chips it is applied to.
13.2.4 Register Settings
VM1
VM0
Function
0
0
Validate – VAL input used to validate a hit
0
1
Calibrate – VAL input used as pulse for calibration
1
0
Time Stamp Reset – VAL input resets the Counter
1
1
VAL input not active – Validate permanently on
13.3 Timing
This circuit generates timing signals for the data register and the ADC.
14 Daisy Control
The daisy chain control sequences the readout of data off chip and from chip to chip. Four chips are
connected in the chain (figure12 and 13).The first chip acts as master and generates the 50MHz
clock which is used to transmit the data. The master also initialises the readout by looking for data
valid signals (DAV) being passed down the chain. The master transmits its own data and the 50MHz
readout clock to the next in the chain, which then passes these on and so on to the last chip in the
chain. When a chip has finished transmitting it passes a read enable token to the next chip in the
chain. The REN signals from each chip remain active until the last in the chain has read out and
passes its REN to the master. The master then releases its REN signal and this propagates along the
chain. The last chip in the chain can output data Manchester Encoded. The number of data packets
output by each chip before passing to the next is programmable up to 256.
14