CS4235 Datasheet, PDF (15/94 Pages) Cirrus Logic – CrystalClear Low Cost ISA Audio System

CS4235
CrystalClear ^TM Low Cost ISA Audio System
PLUG AND PLAY
The Plug-and-Play (PnP) interface logic is com-
patible with the Intel/Microsoft Plug-and-Play
specification, version 1.0a, for an ISA-bus de-
vice. Since the part is an ISA-bus device, it only
supports ISA-compatible IRQs and DMA chan-
nels. Plug and Play compatibility allows the PC
to automatically configure the part into the sys-
tem upon power up. Plug and Play capability
optimally resolves conflicts between Plug and
Play and non-Plug and Play devices within the
system. Alternatively, the PnP feature can be by-
passed. See the Bypassing PnP section for more
information. For a detailed Plug-and-Play proto-
col description, please refer to the Plug and Play
ISA Specification.
To support Plug-and-Play in ISA systems that do
not have a PnP BIOS or a PnP-aware operating
system, the Configuration Manager (CM) TSR
and an ISA Configuration Utility (ICU) from In-
tel Corp. are used to provide these functions.
The CM isolates the cards, assigns Card Select
Numbers, reads PnP card resource requirements,
and allocates resources to the cards based on
system resource availability. The ICU is used to
keep the BIOS and the CM informed of the cur-
rent system configuration. It also aids users in
determining configurations for non-PnP ISA
cards. A more thorough discussion of the Con-
figuration Manager and the ISA Configuration
Utility can be found in the Product Development
Information document of the Plug and Play Kit
by Intel Corp. In a PnP BIOS system, the BIOS
is responsible for configuring all system board
PnP devices. Some systems require additional
software to aid the BIOS in configuring PnP ISA
cards. The PnP BIOS can execute all PnP func-
tions independently of the type of operating
system. However, if a PnP aware operating sys-
tem is present, the PnP responsibilities are shared
between the BIOS and the operating system. For
more information regarding PnP BIOS, please
DS252PP2
refer to the latest revision of the Plug and Play
BIOS Specification published by Compaq Com-
puter, Phoenix Technologies, and Intel.
The Plug and Play configuration sequence maps
the various functional blocks of the part (logical
devices) into the host system address space and
configures both the DMA and interrupt channels.
The host has access to the part via three 8-bit
auto-configuration ports: Address port (0279h),
Write Data port (0A79h), and relocatable Read
Data port (020Bh - 03FFh). The read data port is
relocated automatically by PnP software when a
conflict occurs. Note that the Address Port can
be moved for motherboard devices. See the Ad-
dress Port Configuration section for more
details.
The configuration sequence is as follows:
1. Host sends a software key which places all
PnP cards in the sleep state (or Plug-and-
Play mode).
2. The CS4235 is isolated from the system using
an isolation sequence.
3. A unique identifier (handle) is assigned to the
part and the resource data is read.
4. After all cards’ resource requirements are de-
termined, the host uses the handle to assign
conflict-free resources
5. After the configuration registers have been
programmed, each configured logical device
is activated.
6. The part is then removed from Plug-and-Play
mode.
Upon power-up, the chip is inactive and must be
enabled via software. The CS4235 monitors
writes to the Address Port . If the host sends a
PnP initiation key, consisting of a series of 32
predefined byte writes, the hardware will detect
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