A Real Time Dot Plot Display With a Long (or Short) Memory
Francis L. Battye
The Walter & Eliza Hall Institute
The original FACS II used a Tektronix storage monitor for display of real time dot plots. Thus, as each cell was detected, a dot was stored on the screen and remained there while a plot accumulated. The screen was cleared manually. These screens were prone to "burn-out", were expensive to replace and are now no longer available.
Therefore, an alternative display unit has been designed, having superior function. The display is based on a solid state Planar screen which is large enough (195mm X 97mm) and of sufficient resolution (512 X 256 pixels) for at least 2 separate dot plots. Cell data is stored in an external memory in chronological order, thus allowing user-selectable display of the last 16, 128, 1024 or 2048 cells or of continuous accumulation.
The unit, which contains its own analog-to-digital converters accepts analog input (held peak height) signals for 8 parameters from the FACS II. Any two pairs of parameters can be selected for display. A trigger pulse is also selected from among "all signals", "deflect left", "deflect right" or "all deflect". In this form, the unit should be compatible with any flow cytometer. The initial design includes a joystick-controlled graphics cursor with a separate digital readout of channel position on either of the dot plots. This feature allows accurate setting of peak positions during daily start-up of the cell sorter.
Since the device's memory requirement is modest compared with currently available memory integrated circuits, the unit, as constructed, contains sufficient excess capacity to be modified, at a later date, to allow alternative selection of histogram displays.