DAN-125 Datasheet, PDF (1/2 Pages) Exar Corporation – EXAR’S XR16L784 COMPARED

DATA COMMUNICATIONS APPLICATION NOTE
DAN125
June 2002
EXAR’S XR16L784 COMPARED WITH THE PHILIPS SC28C94 AND SC28L194
Author: PY
1.0 INTRODUCTION
This application note describes the hardware and firmware-related differences between Exar’s XR16L784 with
the Philips SC28C94 and SC28L194. The Exar and Philips QUARTs are very different devices.
1.1 HARDWARE DIFFERENCES
• The XR16L784 is available in the 64-pin TQFP package, while the SC28C94 is available in the 48-pin PDIP
and 52-pin PLCC packages and the SC28L194 is available in the 68-pin PLCC and 80-pin LQFP packages.
• The XR16L784’s 64-pin TQFP package is thinner (1.4 mm) than the SC28L194’s 80-pin LQFP package
(1.75 mm). Also, the Philips LQFP package has longer leads (Lp: 0.55mm min; 0.95 mm max) than Exar’s
TQFP package (L: 0.45 mm min; 0.75 mm max).
• The XR16L784 can operate at either 5 V or 3.3 V with 5 V tolerant inputs. The SC28C94 is a 5 V only device
and the SC28L194 can operate at 5 V or 3.3 V, but it does not have 5 V tolerant inputs at 3.3 V.
1.2 FIRMWARE DIFFERENCES
• The XR16L784 has an industry standard register set while the SC28C94 and SC28L194 has a completely
different register set. The first 8 registers of each channel of the XR16L784 are compatible to industry stan-
dard 16C550 while the registers in the Philips QUARTs are not. The next 8 registers of the XR16L784 are
the enhanced feature registers.
• In the XR16L784, the global registers are separated from the individual channel registers. But in the
SC28C94 and SC28L194, the global registers are mixed in with the individual channel registers.
• The XR16L784 has the ability to write to all channels simultaneously for smaller and quicker initialization rou-
tines. Once simultaneous write has been enabled for the XR16L784, writing to any channel register will write
to the same register of all channels. In the SC28C94 and SC28L194, it is necessary to initialize each chan-
nel individually taking more time to start up.
• The interrupt scheme of the XR16L784 is the same interrupt scheme used in the industry standard 16C550
but with some enhancements like the ability to clear an interrupt in all channels per interrupt service by read-
ing the Global Interrupt Status Registers. On the other hand, the SC28C94 and SC28L194 use a complex
bidding system that the end user will have to understand thoroughly before they can use it effectively. Also,
only the highest interrupt of the highest channel can only be cleared per interrupt service.
• The XR16L784 has a much larger FIFO of 64 bytes compared to the 16 and 8 byte FIFOs in the SC28L194
and SC28C94 respectively, therefore the number of characters taken out of (or loaded into) the FIFO will be
significantly more per interrupt. The ability to load/unload more data reduces CPU bandwidth requirement.
• The XR16L784 has programmable FIFO Trigger Levels of 1 through 64 to optimize the performance for each
individual application. The SC28C94 and SC28L194 both only have 4 Selectable Trigger Levels.
• In addition to Automatic RTS/CTS Hardware Flow Control, the XR16L784 also supports Automatic DTR/
DSR Hardware Flow Control. This gives hardware designers flexibility in selecting which signals to use for
hardware flow control. This feature is not available in the Philips QUARTs.
• The XR16L784 has Automatic 1 or 2 character Xon/Xoff Software Flow Control. In the Automatic 1 character
Xon/Xoff Software Flow Control, an Xoff will be sent to the remote transmitter when the local RX FIFO
reaches the trigger level to halt remote data transmission. An Xon will be sent when the local RX FIFO falls
below the the trigger level to resume remote data transmission. In Automatic 2 character Xon/Xoff Software
Flow Control, two Xoff and Xon characters are sent at the appropriate times instead of just a single charac-
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