CS4235 Datasheet, PDF (16/94 Pages) Cirrus Logic – CrystalClear Low Cost ISA Audio System

CS4235
CrystalClear ^TM Low Cost ISA Audio System
the key and place the part into the Plug-and-Play
(PnP) mode. Another method to program the part
is to use a special Crystal initiation key which
functions like the PnP initiation key, but can be
invoked by the user at any time. However, the
Crystal Key only supports one Audio Codec per
system. The Crystal key and special commands
are detailed in the Crystal Key and Bypassing
PnP sections.
The isolation sequence uses a unique 72-bit se-
rial identifier. The host performs 72 pairs of I/O
read accesses to the Read Data port. The identi-
fier determines what data is put on the data bus
in response to those read accesses. When the iso-
lation sequence is complete, the CM assigns a
Card Select Number (CSN) to the part. This
number distinguishes the CS4235 from the other
PnP devices in the system. The Configuration
Manager (CM) then reads the resource data from
the CS4235. The 72-bit identifier and the re-
source data is either stored in an external
user-programmable E²PROM, or loaded via a
"hostload" procedure from BIOS before PnP
software is initiated.
The CM determines the necessary resource re-
quirements for the system and then programs the
part through the configuration registers. The con-
figuration register data is written one logical
device at a time. After all logical devices have
been configured, CM activates each device indi-
vidually. Each logical device is now available on
the ISA bus and responds to the programmed
address range, DMA channels, and interrupts that
have been allocated to that logical device.
PnP Data
Hardware Configuration and Plug-and-Play re-
source data can be loaded into the part’s RAM.
The data may be stored in an external E²PROM
or may be downloaded from the host. Internal
default PnP data is provided for motherboard de-
signs.
To load the data, refer to the Loading Resource
Data section. The following is the Plug-and-Play
resource data:
The first nine bytes of the PnP resource data are
the Plug-and-Play ID, which uniquely identifies
the Audio Codec from other PnP devices. The
PnP ID is broken down as follows:
0Eh, 63h - Crystal ID - ’CSC’ in compressed
ASCII. (See the PnP Spec for more
information)
42h - OEM ID. A unique OEM ID must be ob-
tained from Crystal for each unique
Crystal product used.
25h - Crystal product ID for the CS4235
FFh, FFh, FFh, FFh - Serial number. This can
be modified by each OEM to uniquely
identify their card.
??h - Checksum.
Of the 9-byte serial number listed above, Cirrus
software uses the first two bytes to indicate the
presence of a CS4235, and the fourth byte, 0x25,
to indicate the CS4235; therefore, these three
bytes must not be altered. The default PnP ID, in
hex, is 0E634236FFFFFFFFA9 for backwards
compatibility.
The next 3 bytes are the PnP version number.
The default is version 1.0a: 0Ah, 10h, 05h.
The next sequence of bytes are the ANSI identi-
fier string. The default is: 82h, 0Eh, 00h,
’Crystal Codec’, 00h.
The logical device data must be entered using
the PnP ISA Specification format. Typical logical
device values are found in Table 1. Internal de-
fault E²PROM data is found in Appendix A.
Loading Resource Data
A serial E²PROM interface allows user-program-
mable serial number and resource data to be
stored in an external E²PROM. The interface is
compatible with devices from a number of ven-
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