TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO
SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999
Terminal Functions (Continued)
TERMINAL
NO.
I/O
DESCRIPTION
NAME
INT2
FN
PN
59
78
O
Printer port interrupt. INT2 is an active-high, 3-state output generated by the positive transition of
ACK. INT2 is enabled by bit 4 of the write control register. Upon reset, INT2 is in the high-impedance
state. Its mode is also controlled by ENIRQ.
IOR
37
36
53
52
I
I
Input/output read strobe. IOR is an active-low input that enables the selected channel to output data
to the data bus (DB0–DB7). The data output depends on the register selected by the address inputs
A0, A1, A2, and chip select. Chip select 0 (CS0) selects ACE #1, chip select 1 (CS1) selects ACE #2,
and chip select 2 (CS2) selects the printer port.
IOW
Input/outputwrite strobe. IOW is an active-low input causing data from the data bus to be input toeither
ACE or to the parallel port. The destination depends on the register selected by the address inputs A0,
A1, A2, and chip selects CS0, CS1, and CS2.
PD0–PD7
PE
53–46
67
72–65 I/O Parallel data bits (0–7). PD0–PD7 provide a byte wide input or output port to the system.
9
I
Line printer paper empty. PE is an input line from the printer that goes high when the printer runs out
of paper.
PEMD
1
11
I
Printer enhancement mode. When low, PEMD enables the write data register to the PD0–PD7 lines.
A high on PEMD allows direction control of the PD0–PD7 port by the DIR bit in the control register.
PEMD is usually tied low for the printer operation.
RESET
39
55
I
Reset. When low, RESET forces the TL16C552A into an idle mode in which all serial data activities
are suspended. The modem control register and its associated outputs are cleared. The line status
register is cleared except for the transmitter holding register empty (THRE) and TEMT bits, which are
set. All functions of the device remain in an idle state until programmed to resume serial data activities.
RESET has a hysteresis level of typically 400 mV.
RTS0,
RTS1
24, 12
9, 61
37, 25
19, 3
O
O
Request to send. The RTS outputs are set low by setting MCR1 of its UARTs modem control register.
Both RTS terminals are reset high by RESET. A low on RTS indicates that its ACE has data ready to
transmit. In half-duplex operations, RTS controls the direction of the line.
RXRDY0,
RXRDY1
Receiver ready. Receiver direct memory access (DMA) signaling is also available through this output.
One of two types of DMA signaling can be selected using FCR3 when in FIFO mode. Only DMA mode
0 is allowed when in TL16C450 mode. For signal transfer DMA (a transfer is made between CPU bus
cycles), mode 0 is used. Multiple transfers that are made continuously until the receiver FIFO has been
emptied are supported by mode 1.
Mode 0. RXRDY is active (low) in FIFO mode (FCR0 = 1, FCR3 = 0) or in TL16C450 mode (FCR0 =
0) and the receiver FIFO or receiver holding register contains at least one character. When there are
no more characters in the FIFO or holding register, RXRDY goes inactive (high).
Mode 1. RXRDY goes active (low) in the FIFO mode (FCR0 = 1) when FCR3 = 1 and the time-out or
trigger levels have been reached. RXRDY goes inactive (high) when the FIFO or holding register is
empty.
RI0, RI1
30, 6
46, 16
57, 4
I
I
I
Ring indicator. The RI signal is a modem control input. Its condition is tested by reading MSR6 (RI) of
each ACE. The modem status register output TERI (MSR2) indicates whether RI has changed from
high to low since the previous reading of the modem status register.
SIN0,
SIN1
41, 62
Serial data. SIN0 and SIN1 move information from the communication line or modem to the
TL16C552A receiver circuits. Mark is a high state and space is a low state. Data on serial data inputs
is disabled in loop mode.
SLCT
SLIN
65
58
7
Line printer select. SLCT is an input line from the printer that goes high when the printer is selected.
77
I/O Line printer select. SLIN is an open-drain I/O that selects the printer when active (low). SLIN has an
internal pullup resistor to V of approximately 10 kΩ.
DD
5
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