Cirrus Logic CS8900A - Manual (Page 104)

104 DS271F5
CS8900A
Crystal LAN™ Ethernet Controller
CIRRUS LOGIC PRODUCT DATASHEET
5.6.9 Rdy4TxNOW vs. Rdy4Tx
The Rdy4TxNOW bit (Register 18, BusST, bit
8) is used to tell the host that the CS8900A is
ready to accept a frame for transmission. This
bit is used during the Transmit Request pro-
cess or after the Transmit Request process to
signal the host that space has become avail-
able when interrupts are not being used (i.e.
the Rdy4TxiE bit (Register B, BufCFG, Bit 8) is
CS8900A Commits
Buffer Space to
Transmit Frame
Host Reads
ISQ
Host Reads the BusST
Register (Register 18)
Transmit Request
Host Writes
Transmit Frame
to CS8900A
Host Writes Transmit Command
to the TxCMD Register
Host Writes Transmit Frame
Length to the TxLength Register
Rdy4Tx
bit = 1?
Exit Transmit Process
No
Yes
No Yes
Rdy4
TxNOW
bit = 1?
Host Enters Interrupt Routine
Exit WAIT-for-interrupt
Process other events
that caused interrupt
No
Yes
Is
TxCMD
pending?
Exit: can't Issue command
Note: Issuing a command
at this point will cause
previous transmit frame
to be lost.
Enter Packet Transmit Process
CS8900A
Transmits Frame
Figure 31. Transmit Operation in Interrupt Mode