Board Initialization
40 – Configuration
VL-486-4 Reference Manual
Board Initialization
Several registers on the VL-386/486 CPU board must be initialized for proper operation. In
DOS-based systems, the BIOS automatically initializes the various registers, however, in non-
DOS-based systems you must program the initialization sequence in ROM. Initialization must
execute immediately upon reset, and in the following order:
•
82C836 Initialization
•
82C721 Initialization
•
486SXLC Initialization
•
RAM Refresh Initialization
If the VL-386/486 is initialized exactly as presented in this manual, the CPU card will be
configured with the following features:
•
16-Bit DMA transfers operate with one wait-state
•
8-Bit DMA transfers operate with one wait-state
•
DRAM operates with zero wait-states
•
ROM active in UMB from 0F0000h to 0FFFFFh
•
Hidden refresh enabled
•
640K + 1M extended DRAM for 2M CPU card
•
640K + 3M extended DRAM for 4M CPU card
•
COM1 is located at I/O address 3F8h
•
COM2 is located at I/O address 2F8h
•
LPT1 is located at I/O address 3BCh
This manual does not document the details of the data written to the chipset registers. Refer to
the Chips & Technologies 82C836 Single-Chip 386sx AT and 82C721 Universal Peripheral
Controller II data books listed in “Other References” on page v.
The chips in the Chips & Technologies chipset, the 82C836 and the 82C721, have different
methods of register access which are described in the following sections.