DP8390 NSC [National Semiconductor], DP8390 Datasheet - Page 19

• Manufacturer Part Number: DP8390
• Description: NIC Network Interface Controller
• Manufacturer: NSC [National Semiconductor]

D3 D4 D5
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 have not been re-
initialized (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 visa 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
D6 D7
Bit
D0
D1
D2
RD0 RD1 RD2
PS0 PS1
Symbol
STP
STA
TXP
00H (READ WRITE)
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 a 1 STP powers up
high
Note If the 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 NIC after either power up or when the 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 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
Note Before the transmit command is given the STA bit must be set and the STP bit reset
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 (pin 29
DIP) 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
7
0
0
0
0
1
0
0
1
1
i) Write a non-zero value into RBCR0
ii) Set bits RD2 RD1 RD0 to 0 0 1
iii) Set RBCR0 1 and RSAR0 1
iv) Issue the Remote Write DMA Command (RD2 RD1 RD0
(Continued)
PS0
6
RD1
PS0
X
0
0
1
1
0
1
0
1
RD2
5
RD0
Register Page 0
Register Page 1
Register Page 2
Reserved
0
1
0
1
X
RD1
4
19
Not Allowed
Remote Read
Remote Write (Note 2)
Send Packet
Abort Complete Remote DMA (Note 1)
RD0
3
TXP
2
Description
STA
1
e
0 1 0)
STP
0