Zx Spectrum Test Program Link -

Unique to the Spectrum, the ULA steals CPU cycles during screen drawing. A subtle bug in a faulty ULA can cause seemingly random crashes only when the screen is being updated. The test program runs a shadow test : writes a pattern to RAM, then repeatedly reads it back during both active display and border periods. If the reads fail only during active display, the ULA’s contention logic or the DRAM’s access time is marginal.

The test program outputs codes in the format: ERROR RAM 0: BIT 3 FAIL . zx spectrum test program link

Developed by , this software was primarily intended as a functional test for the machine's hardware capabilities. Unlike modern diagnostic ROMs that target deep chip-level failures, this program focuses on validating the visible and audible functions of the 48K hardware. Unique to the Spectrum, the ULA steals CPU