Cirrus Logic AN181 - Manual (Page 2)

AN181
2 AN181REV1
ing the high order byte, 00h, to 305h. Next write
0051h (81 decimal) to the TxLENGTH port. Low
byte, 51h, to 306h then high byte, 00h, to 307h.
Now check to see if transmit space is available.
This is done by checking the BusST register, bit 8.
To check this register you will use the packet page
pointer port and the packet page data port.
Write 0138h to Packet Page Pointer (starts at 30Ah)
then read the Packet Page Data Port 0 (starts at
30Ch). If bit 8 (Rdy4TxNow) is set then you can
start transferring data to Transmit Data Port 0. Do
so in the following manner: write the first byte to
300h, the second byte to 301h, byte 3 to 300h, byte
4 to 301h and so on until the whole frame is written.
The chip will automatically send the frame after the
last byte is written.
Frame Reception
The host is notified of an incoming frame by poll-
ing the Rx Event Register. When the host is aware
of an incoming frame the software should read the
frame data following these steps (assuming I/O
base 300h):
• read the RxStatus word (same data as RxEvent,
register) from data port 0. Read this high order
byte 301h first, then low order byte 300h.
Note: it is very important to read the RxStatus
and RxLength high order byte first.
• read the RxLength word (the frame length)
from data port 0. Read this high order byte
301h first, then low order byte 300h.
• begin reading the frame data, 300h then 301h,
300h then 301h until the entire frame has been
transferred to host memory.
Schematic and Layout Review Service
Prevent problems early in the design phase of your
product. Have your schematic or layout reviewed
free of charge by our experts before you build your
board. Call Applications Engineering at (512) 442-
7555 or send e-mail to [email protected]
rus.com.
Unsupported functions in 8 bit mode
• Interrupts are not supported. Polled mode must
be used.
• The DMA engine only uses 16 bit memory ac-
cesses and does not support 8 bit transfers.
• The packet page pointer has an auto increment
feature that cannot be used in 8 bit mode.
• An EEPROM is not supported. Most 8 bit de-
signs should not require one and can eliminate
the added cost.
Contacting Cirrus Logic Support
For a complete listing of Direct Sales, Distributor, and Sales Representative contacts, visit the Cirrus Logic web site at:
http://www.cirrus.com/corporate/contacts/
Crystal is a trademark of Cirrus Logic, Inc.
Linux is a registered trademark of Linus Torvalds
PSOS is register trademark of Integrated System Inc.
VxWorks is a registered trademark of Wind River Systems, Inc.
All other names are trademarks, registered trademarks, or service marks of their respective companies.
Preliminary product information describes products which are in production, but for which full characterization data is not yet available. Advance product infor-
mation describes products which are in development and subject to development changes. Cirrus Logic, Inc. has made best efforts to ensure that the information
contained in this document is accurate and reliable. However, the information is subject to change without notice and is provided “AS IS” without warranty of
any kind (express or implied). No responsibility is assumed by Cirrus Logic, Inc. for the use of this information, nor for infringements of patents or other rights
of third parties. This document is the property of Cirrus Logic, Inc. and implies no license under patents, copyrights, trademarks, or trade secrets. No part of
this publication may be copied, reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photographic, or
otherwise) without the prior written consent of Cirrus Logic, Inc. Items from any Cirrus Logic website or disk may be printed for use by the user. However, no
part of the printout or electronic files may be copied, reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical,
photographic, or otherwise) without the prior written consent of Cirrus Logic, Inc.Furthermore, no part of this publication may be used as a basis for manufacture
or sale of any items without the prior written consent of Cirrus Logic, Inc. The names of products of Cirrus Logic, Inc. or other vendors and suppliers appearing
in this document may be trademarks or service marks of their respective owners which may be registered in some jurisdictions. A list of Cirrus Logic, Inc. trade-
marks and service marks can be found at http://www.cirrus.com.