DESCRIPTION
In the unidirectional modes, an associated data direction register determines whether each port pin is an input or output. In the bidirectional modes the data direction registers are ignored and the direction is determined dynamically by the state of four handshake pins. The PI/T ports allow use of vectored or auto-vectored interrupts, and also provide a DMA request pin for connection to the 68440 direct memory access controller (DMAC) or a similar circuit. The PI/T timer contains a 24-bit wide counter and a 5-bit prescaler. The timer may be clocked by the system clock (PI/T CLK pin) or by an external clock (TIN pin), and a 5-bit prescaler can be used. It can generate periodic interrupts, a square wave, or a single interrupt after a programmed time period. It can also be used for elapsed time measurement or as a device watchdog. January 1989 1/61 TS68230 SECTION 1 INTRODUCTION The TS68230 parallel interface/timer (PI/T) provides versatile double buffered parallel interfaces and a system oriented timer for TS68000 systems.
STMicroelectronics
