Motorola MVME166IG/D2 - Manual (Page 24)

Board Level Hardware Description
1-10 MVME166 Single Board Computer Installation Guide
1
Data Bus Structure
The local data bus on the MVME166 is a 32-bit synchronous bus that is based
on the MC68040 bus, and supports burst transfers and snooping. The various
local bus master and slave devices use the local bus to communicate. The local
bus is arbitrated by priority type arbiter and the priority of the local bus
masters from highest to lowest is: 82596CA LAN, CD2401 serial (through the
PCCchip2), 53C710 SCSI, VSB, VMEbus, and MPU. In the general case, any
master can access any slave; however, not all combinations pass the common
sense test. Refer to the MVME166/MVME167/MVME187 Single Board
Computers Programmer’s Reference Guide and to the user’s guide for each device
to determine its port size, data bus connection, and any restrictions that apply
when accessing the device.
MC68040 MPU
The MC68040 processor is used on the MVME166. The MC68040 has on-chip
instruction and data caches and a floating point processor. Refer to the
M68040 user’s manual for more information.
Flash Memory and Download EPROM
The MVME166 includes four 28F020 Flash memory devices and a download
EPROM. These parts replace the four EPROM sockets used on the
MVME167/187. The Flash parts are programmable on the MVME166 board
and the programming code is provided in the download EPROM. The Flash
devices provide 1 MB of ROM at address $FF800000-$FF8FFFFF. The
download EPROM provides 128 KB of ROM at $FFF80000-$FFF9FFFF. The
download EPROM is mapped to local bus address 0 following a local bus reset.
This allows the MC68040 to access the stack pointer and execution address
following a reset. The download EPROM appears at 0 until the DR0 bit is
cleared in the PCCchip2 chip. The Flash devices are controlled by the
VMEchip2 and the download EPROM is controlled by the PCCchip2. The PC0
bit in the MC68230 PI/T chip must be low to enable writes to Flash.
The EPROM contains the BootBug product (166BBug). Because Flash memory
can be electronically erased, the EPROM firmware is a subset of the regular
debugger product. It contains enough functionality from the debugger to
permit downloading of object code (via VMEbus, serial port, SCSI bus, or the
network) and reprogramming of the Flash memory.
A jumper on the MVME166 (J3, pins 7 and 8) controls the operation of the
BootBug. If the jumper is in place, the BootBug (which always executes at
power-up and reset) passes execution to the full debugger contained in Flash
memory. If the jumper is removed, execution continues (with diminished
functionality) in the BootBug.