Specifications

Appendix F: Registers
75
VME A21–16 Address Register (8130h)
When the EPC-8A performs an access in its “E page” (address range 0E0000–0EFFFF),
the access is mapped onto the VMEbus. The least-significant sixteen of the VME address
bits are provided directly (from the 486), and the remaining 8 (for an A24 access) or 16
(for an A32 access) bits must come from somewhere else. Six come from this register:
Bit 7 of this register is used as VME address bit 21, bit 6 as VME address bit 20, ..., and bit
2 as VME address bit 16.
The two low-order bits are ROM bits. For compatibility with older EPCs, this register is
aliased at I/O port addresses 8132, 8134, and 8136.
ID Register (8140h and 8141h)
This read-only register adheres to the VXIbus specification. It defines the EPC-8A as a
message-based device and the manufacturer as RadiSys Corporation.
Device Type Register (8142h and 8143h)
This register adheres to the VXIbus specification. The value defines the EPC-8A as
having a model code of 0C4h if it is a slot 0 controller and 1C4h if it is not a slot 0
controller). Note that the S bit is a read/write bit that must be set by BIOS very early in the
boot sequence. This bit may also be read/written from the VME port.
Status/Control Register (8144h and 8145h)
This register adheres to the VXIbus specification and also contains EPC-8A specific bits.
SRIE SYSRESET input enable. If set, assertion of VME SYSRESET generates a
reset of the EPC-8A. One use of this bit is having EPC-8A software reset other
VME devices (via bit SYSR) without resetting the EPC-8A. This bit may be
read/written from the PC port, but is read-only from the VME port.
SYSCLK SYSCLK status bit. Only PC port writes to this register can clear this bit. The
VMEbus Address bits 21–16 1 1
Register bit VME address bit
721
620
216
Lower
11101100
Upper
10111111
Lower
11000100
Upper
000000S
Lower
SRIE 1 SYSC 1 READY PASS NOSF SRST
Upper
0 MODID SYSR R RESDET 1 1 1