TL16PC564B, TL16PC564BLV

PCMCIA UNIVERSAL ASYNCHRONOUS RECEIVER TRANSMITTER

SLLS225A – MARCH 1996 – REVISED FEBRUARY 1998

10

POST OFFICE BOX 655303

host CPU/UART interface

The UART select is derived from either host CPU address information or logic levels on CE1, CE2 and REG.

In the address mode, host CPU address bits HA9, HA7, HA6, HA5, and HA3 are combined with conditional

derivatives of HA4 and HA8 to select the UART (HA4 and HA8 select COM ports 1 – 4 based on settings in the

subsystem control register). CE1 and CE2 are combined such that either of these two signals in combination

with REG enable the UART in the event that these signals are present. In the event that CE1 or CE2 are not

present, the UART must be accessed in the address mode previously described. The UART select in

conjunction with IORD and IOWR allows host CPU accesses to the UART. Host CPU address bits HA2–HA0

are decoded to select which UART register is to be accessed.

All UART registers remain intact with the exception of the FIFO control register (FCR) and the modem-control

register (MCR). The FCR (host CPU write-only address 2) bits 4 and 5 in conjunction with EXTEND control RTS

operation and FIFO depth as follows:

BIT 5

BIT 4

EXTEND

RTS OPERATION

FIFO DEPTH

X

X

H

Normal

16 bytes

0

0

L

Normal

16 bytes

0

1

L

Auto

16 bytes

1

0

L

Normal

64 bytes

1

1

L

Auto

64 bytes

FCR bit 5 high and EXTEND low redefine the receiver FIFO trigger levels set by FCR bits 6 and 7 as follows:

BIT 7

BIT 6

TRIGGER LEVEL

0

0

1

0

1

16

1

0

32

1

1

56

The MCR (host CPU address 4) bit 5 is read only. Bit 5 is controlled by the subsystem to enable (high) the

auto-CTS mode of operation

subsystem/UART interface

The UART provides a serial-communications channel to the subsystem with enhanced RTS control (see

auto-RTS description). This channel is capable of operating at 115 kbps and is the main communications

channel to the subsystem (refer to the TL16C550 specification for the detailed description of the

serial-communications channel).

Many of the UART registers have been mapped into the subsystems memory space as read only. In addition,

MCR bit 5 (subsystem address 130 hex) is controlled by the subsystem to enable (high) auto-CTS. The

subsystem can read the MCR at address 134 hex. When reading the FCR (subsystem address 132 hex), bits

1 and 2 are always high, and bits 4 and 5 are low only when EXTEND is low and the host CPU has set them

high (64-byte FIFOs and auto-RTS enabled) (refer to the subsystem memory map).