TREC: A tool kit for programming cognitive experiments in Applesoft BASIC

Screen display and timing synchronization on the Apple IIe and Apple Ilgs

“…This use of the VBL assures the longest possible time in which to transfer information to screen memory. Sanmartin (1987) employs this technique, which is also mentioned by Reed (1979). (2) Other programs (e.g., Diener & Smee, 1984) write the stimuli characters to a "hidden" screen memory area (a screen memory area other than the one currently displayed), then wait for the offset of a VBL before switching screen display pages and starting a timer.…”

“…On the Apple lIe, this is accomplished with the monitoring of memory location $COI9, called RDVBLBAR, which holds the status of the vertical blanking interval (VEL). I Procedures for monitoring the VBL to synchronize displays on the Apple 11+ and Apple lIe have become available (e.g., Adams, 1985;Cavanagh & Anstis, 1980;Dorfman, 1987;Reed, 1979;Sanmartin, 1987).…”