Motorola MVME147 Installation And Use Manual page 144

Functional Description
Sources of Bus Error (BERR*)
Local Bus Time-Out
5
VMEbus Access Time-Out
VMEbus BERR*
5-28
The devices on the MVME147 that are capable of activating a local
bus error are described below.
A Local Bus Time-Out (LBTO) occurs whenever an MPU or PCC
access (outside of the VMEbus range) does not complete within the
programmed time. If the system is configured properly, this should
only happen if software accesses a nonexistent location within the
onboard address range. Whenever an LBTO occurs, the LBTO
status bit is set in the VMEchip.
A VMEbus Access Time-Out (VATO) occurs whenever a PCC or
MC68030 VMEbus bound cycle does not receive a VMEbus Bus
Grant within the programmed time. This is usually caused by
another bus master holding the bus for an excessive period of time.
When a VATO occurs, the VATO status bit is set in the VMEchip.
The VMEbus BERR* occurs when the BERR* signal line is activated
on the VMEbus while the MC68030 or PCC is the VMEbus master.
VMEbus BERR* should occur only if:
An initialization routine samples to see if a device is present
on the VMEbus and it is not.
Bad software accesses a nonexistent device within the
VMEbus range.
Bad configuration tries to access a device on the VMEbus
incorrectly (such as driving LWORD* low to a 16-bit board).
A hardware error occurs on the VMEbus.