Motorola MVME177 manual Module Identification, Timing Performance, Local Bus Time-out

4

Functional Description

Local Bus Time-out

The MVME177 provides a time-out function for the local bus. When the timer is enabled and a local bus access times out, a Transfer Error Acknowledge (TEA) signal is sent to the local bus master. The time-out value is selectable by software for:

❏8 ∝sec

❏64 ∝sec

❏256 ∝sec

❏Infinite

The local bus timer does not operate during VMEbus bound cycles. VMEbus bound cycles are timed by the VMEbus access timer and the VMEbus global timer. Refer to the VMEchip2 in the Single Board Computers Programmer's Reference Guide for detailed programming information.

Module Identification

Software distinguishes between an MVME177 module and an MVME176 module by use of the I/O control register (GPI) bit 3. On an MVME177, the I/O control register (GPI) bit 3 is out (open) for a ÒhighÓ (one). On an MVME176, the I/O control register (GPI) bit 3 is hardwired in (shorted) for a ÒlowÓ (zero).

Timing Performance

This section provides the performance information for the MVME177. Various MVME177s are designed to operate at 50 MHz or 60 MHz (when supported by 060).

Local Bus to DRAM Cycle Times

The PCCchip2 and VMEchip2 have the same local bus interface timing as the MC68060, therefore the following cycle times also apply to the PCCchip2 and the VMEchip2. Read accesses to

4-18