SC26L198 Philips Semiconductors, SC26L198 Datasheet - Page 5

• Manufacturer Part Number: SC26L198
• Description: Octal UART with TTL compatibility at 3.3V and 5V supply voltages
• Manufacturer: Philips Semiconductors

Philips Semiconductors
BLOCK DIAGRAM
As shown in the block diagram, the Octal UART consists of: an
interrupt arbiter, host interface, timing blocks and eight UART
channel blocks. The eight channels blocks operate independently,
interacting only with the timing, host I/F and interrupt blocks.
FUNCTIONAL DESCRIPTION
The SC26C198 is composed of several functional blocks:
CONCEPTUAL OVERVIEW
Host Interface
The Host interface is comprised of the signal pins CEN, W/RN,
IACKN, DACKN, IRQN Sclk and provides all the control for data
transfer between the external and internal data buses of the host
and the OCTART. The host interface operates in a synchronous
mode with the system (Sclk) which has been designed for a nominal
operating frequency of 33 MHz. The interface operates in either of
two modes; synchronous or asynchronous to the Sclk However
the bus cycle within the OCTART always takes place in four Sclk
1995 May 1
Synchronous host interface block
A timing block consisting of a common baud rate generator
making 22 industry standard baud rates and 2 16–bit counters
used for non–standard baud rate generation
4 identical independent full duplex UART channel blocks
Interrupt arbitration system evaluating 24 contenders
I/O port control section and change of state detectors.
Octal UART with TTL compatibility at 3.3V
and 5V supply voltages
INPUT BUFFERS AND OUTPUT DRIVERS
Block Diagram SC26/68C198
FULL DUPLEX UART CHANNEL
FULL DUPLEX UART CHANNEL
FULL DUPLEX UART CHANNEL
FULL DUPLEX UART CHANNEL
FULL DUPLEX UART CHANNEL
FULL DUPLEX UART CHANNEL
FULL DUPLEX UART CHANNEL
FULL DUPLEX UART CHANNEL
340
cycles after CEN is recognized. These four cycles are the C1, C2,
C3, C4 periods shown in the timing diagrams. DACKN always
occurs in the C4 time and occurs approximately 18 ns after the
rising edge of C4.
Addressing of the various functions of the OCTART is through the
address bus A(7:0). The 26C198 is compatible with the SC28L194
Quad UART in software and function. A[7], in a general sense, is
used to separate the data portion of the circuit from the control
portion.
Asynchronous bus cycle
The asynchronous mode requires one bus cycle of the chip select
(CEN) for each read or write to the chip. No more action will occur
on the bus after the C4 time until CEN is returned high.
Synchronous bus cycle
In the synchronous mode a read or write will be done every four
cycles of the Sclk. CEN does not require cycling but must remain
low to keep the synchronous accesses active. This provides a burst
mode of access to the chip.
In both cases each read or write operation(s) will be completed in
four (4) Sclk cycles. The difference in the two modes is only that the
asynchronous mode will not begin another bus cycle if the CEN
remains active after the four internal Sclk have completed. Internally
the asynchronous cycle will terminate after the four periods of Sclk
regardless of how long CEN is held active
In all cases the internal action will terminate at the withdrawal of
CEN. Synchronous CEN cycles shorter than multiples of four Sclk
cycles minus 1 Sclk and asynchronous CEN cycles shorter than four
Sclk cycles may cause short read or write cycles and produce
corrupted data transfers.
SC26C198 SC68C198
SC26L198 SC68L198
Product specification
SD00193