83C795 Datasheet, PDF (33/136 Pages) List of Unclassifed Manufacturers – Ethernet System Controller

83C795
ETHERNET SYSTEM CONTROLLER REGISTERS
BIT
7
6
5
4
3
2
1
0
IAR
IA15
IA14
IA13
IA8
IA7
IA6
IA5
PNPBOOT
RESET
0
0
0
0
1
0
0
0
INIT
0
0
0
0
1
0
0
0
Bits 7-5: IA15-IA13, I/O Address Lines
T hes ebits arecomparedagains t theA15-A13 lines
fromthehost when IOR or IOW areactiveandAE N
is not. To acces s the chip, the lines mus t match.
Bits 4-1: IA8-IA5, I/O Address Lines
T hes e bits are compared agains t the A8-5 lines
fromthehost when IOR or IOW areactiveandAE N
is not. To acces s the chip, the lines mus t match.
Bit 0: PNPBOOT, Plug and Play Boot Bit
PNPBOOT = 1 to indicate to the Plug and Play
hardware that the adapter is a boot card. T his
allows the 83C795 address decoders to be active
without waiting for the Plug and Play hardware
activate command.
5.1.14 RAR - RAM Address Register
R ead/Write Port = OB S WH=1
T his regis ter controls thebas eaddres s andwindow
s ize for the buffer R AM.
BIT
7
6
5
4
3
2
1
0
RAR
HRAM
RA17
RAMSZ1
RAMSZ0
RA16
RA15
RA14
RA13
RESET
0
0
0
0
0
1
0
0
INIT
0
0
0
0
0
1
0
0
Bit 7: HRAM, High RAM Address
T his bit provides a means of locating the buffer
memory above the 1MB DOS limit. When HR AM =
0, the buffer addres s decoder matches LA23-LA20
agains t zero. When HR AM = 1, the LA23-LA20
lines are matched agains t the value F. T his field is
not s upported by the Plug and Play hardware.
Bits 5-4: RAMSZ1-RAMSZ0, Buffer Window Size
Field
T his encoded field determines the apparent s ize of
the buffer R AM. It is decoded in the following man-
ner:
SZ1
0
0
1
1
SZ0
0
1
0
1
Window Size
8K Bytes
16K Bytes
32K Bytes
64K Bytes
TABLE 5-5. BUFFER WINDOW SIZE FIELD
Bits 6, 3-0: RA17, RA16-RA13, RAM Base
Address Field
T hes e bits form part of the bas e addres s for the
buffer R AM decoder along with the fixed value of
’11’ for R A19-R A18. When S A19-S A13 has avalue
between this base addres s and the base plus the
windows ize, the reques t for memory is recognized.
Once the S A19-S A13 value is no longer in this
range, the host ends the acces s .
Note
The 64K window size is not supported
by Plug and Play.
5.1.15 BIO - ROM Control Register
R ead/Write Port = 0C S WH = 1
T his regis ter programs the bas e addres s and
window s ize for the external R OM.
BIT
7
6
5
4
3
2
1
0
BIO
FINE16
BA17
BIOSZ1
BIOSZ0
BA16
BA15
BA14
BA13
RESET INIT RECALL
0
0 EE
0
0 EE
1
1 EE
1
1 EE
0
0 EE
0
0 EE
0
0 EE
0
0 EE
20