
10.0 Legacy Functional Blocks
(Continued)
Revision 1.2
225
www.national.com
P
10.3 SERIAL PORTS (SP1 AND SP2)
10.3.1
The identical Serial Port functional blocks SP1 and SP2 both support serial data communication with a remote peripheral
device or modem using a wired interface. The Serial Ports can function in one of three modes:
General Description
G
16450-Compatible mode (Standard 16450)
G
16550-Compatible mode (Standard 16550)
G
Extended mode
Extended mode provides advanced functionality for the UART.
The Serial Ports provide receive and transmit channels that can operate concurrently in full-duplex mode. They perform all
functions required to conduct parallel data interchange with the system and composite serial data exchange with the external
data channel, including:
G
Format conversion between the internal parallel data format and the external programmable composite serial format
G
Serial data timing generation and recognition
G
Parallel data interchange with the system using a choice of bidirectional data transfer mechanisms
G
Status monitoring for all phases of communication activity
G
Complete MODEM-control capability.
Existing 16550-based legacy software is completely and transparently supported. Module organization and specific fallback
mechanisms switch the module to 16550-Compatible mode on reset or when initialized by 16550 software.
10.3.2
Four register banks, each containing eight registers, control Serial Port operation. All registers use the same 8-byte address
space to indicate offsets 00h through 07h. The active bank must be selected by the software.
The register bank organization enables access to the banks as required for activation of all module modes, while maintaining
transparent compatibility with 16450 or 16550 software.
The Bank Selection register (BSR) selects the active bank and is common to all banks as shown in Figure 52. Therefore,
each bank defines seven new registers.
The default bank selection after system reset is 0.
Register Bank Overview
Figure 52. Register Bank Architecture
BANK 0
BANK 1
BANK 2
BANK 3
Offset 07h
Offset 06h
Offset 05h
Offset 04h
LCR/BSR
Offset 02h
Offset 01h
Offset 00h
Common
Register
Throughout
All Banks
16550 Banks