CS4235 Datasheet, PDF (18/94 Pages) Cirrus Logic – CrystalClear Low Cost ISA Audio System

the External E²PROM section for more informa-
tion on the serial E²PROM interface and
E²PROM programming.
The format for the data stored in the E²PROM is
as follows:
2 bytes E²PROM validation: 55h, BBh
2 bytes length of resource data in E²PROM
19 bytes Hardware Configuration
9 bytes Plug and Play ID
3 bytes Plug and Play version number
Variable number of bytes of user defined
ASCII ID string
Logical Device 0 (Windows Sound System,
FM Synthesizer, Sound Blaster Pro) data
Logical Device 1 ( Game Port) data
Logical Device 2 ( Control) data
Logical Device 3 ( MPU-401) data
Logical Device 4 ( CD-ROM) data
End of Resource byte & checksum byte
Firmware patch code.
The default internal E²PROM data, in assembly
format, can be found in Appendix A.
Loading Firmware Patch Data
An external E²PROM is read during the power-
up sequence that stores Hardware Configuration
and PnP data, and firmware patch data. The part
contains RAM and ROM to run the core proces-
sor. The RAM allows updates to the core
processor functionality. Placing the firmware
CS4235
CrystalClear ^TM Low Cost ISA Audio System
patches in E²PROM, gives the maximum func-
tionality at power-up without the need for a
software driver.
The firmware patch data is typically included at
the end of the PnP resource data. Cirrus provides
a utility that will read in patch data from a file,
and append it to the PnP resource data. The
patch file must be obtained from Cirrus.
The Crystal Key
NOTE: The Crystal Key cannot differentiate be-
tween multiple Cirrus Audio Codecs in a system;
therefore, ONLY ONE audio part is allowed in
systems using the Crystal Key. To allow multiple
parts in a system, the Plug-and-Play isolation se-
quence must be used since it supports multiple
parts via the serial identifier used in the isolation
sequence. Crystal Key 2 is also designed to al-
low motherboard and add-in card chips to
co-exist in a system.
The Crystal key places the part in the configura-
tion mode. Once the Crystal key has been
initiated, an alternate method of programming
the configuration registers may be used. This al-
ternate method is referred to as the "SLAM"
method. The SLAM method allows the user to
directly access the configuration registers, con-
figure, and activate the chip, and then,
optionally, disable the PnP and/or Crystal key
feature. The SLAM method uses commands that
are similar to the PnP commands; however, they
are different since the user has direct access to
the configuration registers. To use the SLAM
method, see the Bypassing PnP section.
The following 32 bytes, in hex, are the Crystal
key:
96, 35, 9A, CD, E6, F3, 79, BC,
5E, AF, 57, 2B, 15, 8A, C5, E2,
F1, F8, 7C, 3E, 9F, 4F, 27, 13,
09, 84, 42, A1, D0, 68, 34, 1A
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DS252PP2