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BIT
7
6
5
4
3
2
1
0
CURRL
RESET
X
X
X
X
X
X
X
X
A07
A06
A05
A04
A03
A02
A01
A00
5.2.9
Linked-List Map Read Port = 2:1E Linked-List Map
Write Port = 0:1E
DCON - Data Configuration Register
This register always returns 41h. In the 83C790 this
register controlled DMA burst lengths; however, the
83C795 is hardwired for 8-byte bursts. Refer to
page 65 for more information.
5.2.10 ENH - Enhancement Register
Normal Map Read/Write Port = 2:17
Linked-List Map Read/Write Port = 2:17
This register enables enhancement features.
BIT
7
6
5
4
3
2
1
0
ENH
RESET
0
1
0
0
0
0
0
0
—
—
ALTEGO
SLOT1
SLOT0
EOTINT
—
SBACK
Bits 7-6: Unused
Bit 5: ALTEGO
, Buffering Format Selection
ALTEGO = 0 -
Designates ring buffering and single frame trans-
mission format. This is essentially 8390/83C690
compatibility mode.
ALTEGO = 1 -
Designates linked-list receive buffering and multi-
ple frame transmission format. The register ad-
dress map is selected with this bit, exposing the
registers associated with the selected buffering
mode.
Bits 4-3: SLOT1-0
, Slot Time Selection
This two-bit field selects the slot time according to
Table 5-10.
SLOT1
0
1
1
SLOT0
X
0
1
Slot Time
512 bit times (Ethernet)
256 bit times
1024 bit times
TABLE 5-9. SLOT TIME SELECTION FIELD
Bit 2: EOTINT
, Interrupt on End-of-Transmit
EOTINT = 1 -
Interrupt on End-of-Transmit chain instead of each
transmitted frame. This bit is ignored if not operating
in multiple frame transmission mode.
EOTINT = 0 -
Interrupt on each transmitted frame.
Bit 0: SBACK
, Enable Stop Backup Modifications
SBACK = 1 -
Enable the Stop Backoff modifications to the back-
off timer.
SBACK = 0 -
Normal backoff.
5.2.11 ERWCNT - Early Receive Warning
Threshold Register
Normal Map Read/Write Port = 0:18
Linked-List Map Read/Write Port = 0:18
This register contains the Received Byte Count
threshold at which the Early Receive Warning
interrupt is generated. The ERW interrupt is
generated when RBC
≥
ERW. Bits 3-0 of RBC are
ignored. For more information on this register, refer
to page 71.
83C795
ETHERNET SYSTEM CONTROLLER REGISTERS
26