TL16PNP550A_08 Datasheet, PDF (20/40 Pages) Texas Instruments – ASYNCHRONOUS COMMUNICATIONS ELEMENT WITH PLUG-AND-PLAY (PnP) AND AUTOFLOW CONTROL

TL16PNP550A
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ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH PLUGĆANDĆPLAY (PnP) AND AUTOFLOW CONTROL
SLLS190B − MARCH 1995 − REVISED MARCH 1996
PRINCIPLES OF OPERATION
PnP card configuration sequence
The PnP logic is quiescent on power up and must be enabled by software. The following sequence configures
the PnP card:
1. The initiation key places the PnP logic into configuration mode through a series of predefined writes to
the ADDRESS port (see autoconfiguration ports section).
2. A serial identifier is accessed bit serially and isolates the Industry Standard Architecture (ISA) cards.
Seventy-two READ_DATA port reads are required to isolate each card.
3. Once isolated, a card is assigned a handle [card select number (CSN)] that later selects the card. This
assignment is accomplished by programming the CSN.
4. The PnP software then reads the resource data structure on each card. When all resource capabilities
and demands are known, a process of resource arbitration is invoked to determine resource allocation
for each card.
5. All PnP cards are then activated and removed from the configuration mode. This activation is
accomplished by programming the ACTIVE register.
PnP autoconfiguration ports
Three 8-bit ports (see Table 4) are used by the software to access the configuration space on each PnP ISA
card. These registers are used by the PnP software to issue commands, check status, access the resource data
information, and configure the PnP hardware.
The ports have been chosen so as to avoid conflicts in the installed base of ISA functions, while at the same
time minimizing the number of ports needed in the ISA I/O space.
Table 4. Autoconfiguration Ports
PORT NAME
ADDRESS
WRITE_DATA
READ_DATA
LOCATION
0×0279 (printer status port)
0×0A79 (printer status port + 0×0800)
Relocatable in range 0×0203 to 0×03FF
TYPE
Write only
Write only
Read only
The PnP registers are accessed by first writing the address of the desired register to the ADDRESS port,
followed by a read of data from the READ_DATA port, or a write of data to the WRITE_DATA port. Once
addressed, the desired register may be accessed using the WRITE_DATA or READ_DATA ports.
The ADDRESS port is also the destination of the initiation key writes.
The address of the READ_DATA port is set by programming the SET RD_DATA PORT register. If a card cannot
be isolated for a given READ_DATA port address, the READ_DATA port address is in conflict. The READ_DATA
port address must then be relocated and the isolation process begun again. The entire range between 0× 0203
and 0 × 3FF is available; however, in practice it is expected that only a few address locations are necessary
before the software determines that no PnP cards are present
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