CS5535-UDCF AMD (ADVANCED MICRO DEVICES), CS5535-UDCF Datasheet - Page 143

• Manufacturer Part Number: CS5535-UDCF
• Manufacturer: AMD (ADVANCED MICRO DEVICES)

Specifications of CS5535-UDCF

• Operating Temperature (min): 0C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Compliant

UART and IR Port
5.12.1.7 Automatic Fallback to 16550 Compatibility
This feature is designed to support existing legacy software
packages, using the 16550 serial port. For proper opera-
tion, many of these software packages require that the
module look identical to a plain 16550, since they access
the serial port registers directly. Because several extended
features and new operational modes are provided, make
sure the module is in the proper state before executing a
legacy program.
The fallback mechanism eliminates the need to change the
state when a legacy program is executed following comple-
tion of a program that used extended features. It automati-
cally switches the module to 16550 compatibility mode and
turns off any extended features whenever the Baud Gener-
ator Divisor Register is accessed through the LBGD_L or
LBGD_H ports in register Bank 1.
In order to avoid spurious fallbacks, baud generator divisor
ports are provided in Bank 2. Baud generator divisor
access through these ports changes the baud rate setting
but does not cause fallback.
New programs designed to take advantage of the extended
features should not use LBGD_L and LBGD_H to change
the baud rate. Instead, they should use BGD_L and
BGD_H.
A fallback can occur in either extended or non-extended
modes. If extended mode is selected, fallback is always
enabled. In this case, when a fallback occurs, the following
happens:
• TX_FIFO and RX_FIFO switch to 16 levels.
• A value of 13 is selected for the baud generator pre-
• ETDLBK and BTEST of the EXCR1 register are cleared.
• UART mode is selected.
• The functional block switches to non-extended mode.
AMD Geode™ CS5535 Companion Device Data Book
scaler.
Mode
When fallback occurs from non-extended mode, only the
first three of the above actions occur. If either Sharp-IR or
SIR infrared modes were selected, no switching to UART
mode occurs. This prevents spurious switching to UART
mode when a legacy program, running in Infrared mode,
accesses the Baud Generator Divisor Register from Bank
1.
Fallback from non-extended mode can be disabled by set-
ting LOCK in the EXCR2 register to 1. When LOCK is set
and the functional block is in non-extended mode, two
scratch pad registers overlaid with LBGD_L and LBGD_H
are enabled. Any attempted processor access of the Baud
Generator Divisor Register through LBGD_L and LBGD_H
accesses the scratch pad registers, without affecting the
baud rate setting. This feature allows existing legacy pro-
grams to run faster than 115.2 Kbaud, without realizing
they are running at this speed.
5.12.2
An MSR (MSR_UART[x]_MOD) (UART1 MSR 51400038h
and UART2 MSR 5140003Ch) mimics modem input sig-
nals for making it compatible with the software having
modem support. The hardware of this module has all the
required functionality for modem compatibility.
Modem Support
31506B
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