dp83902a National Semiconductor Corporation, dp83902a Datasheet - Page 26

• Manufacturer Part Number: dp83902a
• Description: St-nictm Serial Network Interface Controller For Twisted Pair
• Manufacturer: National Semiconductor Corporation

and
and
D3
D4
Bit
D0
D1
D2
D5
D6
D7
10 0 Internal Registers
10 3 REGISTER DESCRIPTIONS
COMMAND REGISTER (CR)
The Command Register is used to initiate transmissions enable or disable Remote DMA operations and to select register
pages To issue a command the microprocessor sets the corresponding bit(s) (RD2 RD1 RD0 TXP) Further commands may
be overlapped but with the following rules (1) If a transmit command overlaps with a remote DMA operation bits RD0 RD1
and RD2 must be maintained for the remote DMA command when setting the TXP bit Note if a remote DMA command is re-is-
sued when giving the transmit command the DMA will complete immediately if the remote byte count register has not been
reinitialized (2) If a remote DMA operation overlaps a transmission RD0 RD1 and RD2 may be written with the desired values
and a ‘‘0’’ written to the TXP bit Writing a ‘‘0’’ to this bit has no effect (3) A remote write DMA may not overlap remote read
operation or vice versa Either of these operations must either complete or be aborted before the other operation may start Bits
PS1 PS0 RD2 and STP may be set any time
Symbol
STP
STA
TXP
RD0
RD1
and
RD2
PS0
and
PS1
Stop Software reset command takes the controller offline no packets will be received or transmitted Any
reception or transmission in progress will continue to completion before entering the reset state To exit this
state the STP bit must be reset and the STA bit must be set high To perform a software reset this bit
should be set high The software reset has executed only when indicated by the RST bit in the ISR being set
to 1 STP powers up high
Note If the ST-NIC has previously been in start mode and the STP is set both the STP and STA bits will remain set
Start This bit is used to activate the ST-NIC after either power up or when the ST-NIC has been placed in a
reset mode by software command or error STA powers up low
Transmit Packet This bit must be set to initiate the transmission of a packet TXP is internally reset either
after the transmission is completed or aborted This bit should be set only after the Transmit Byte Count and
Transmit Page Start registers have been programmed
Remote DMA Command These three encoded bits control operation of the Remote DMA channel RD2
can be set to abort any Remote DMA command in progress The Remote Byte Count Registers should be
cleared when a Remote DMA has been aborted The Remote Start Addresses are not restored to the
starting address if the Remote DMA is aborted
RD2
Note 1 If a remote DMA operation is aborted and the remote byte count has not decremented to zero PRQ will remain high A read
acknowledge (RACK) on a write acknowledge (WACK) will reset PRQ low
Note 2 For proper operation of the Remote Write DMA there are two steps which must be performed before using the Remote Write
DMA The steps are as follows
Page Select These two encoded bits select which register page is to be accessed with addresses RA0 – 3
PS1
0
0
0
0
1
0
0
1
1
III) Set RBCR0 1 and RSAR0 1
IV) Issue the Remote Write DMA Command (RD2 RD1 RD0
II) Set bits RD2 RD1 and RD0 to 0 0 and 1
I) Write a non-zero value into RBCR0
RD1
PS0
0
0
1
1
X
0
1
0
1
00H (READ WRITE)
PS1
7
RD0
Register Page 0
Register Page 1
Register Page 2
Reserved
(Continued)
0
1
0
1
X
PS0
6
Not Allowed
Remote Read
Remote Write (Note 2)
Send Packet
Abort Complete Remote DMA (Note 1)
RD2
5
RD1
4
26
RD0
3
Description
e
0 1 0)
TXP
2
STA
1
STP
0