Xycom XVME-400, Manual

Page: 34 / 83

XVME-400/40l/490/491 Manual
October, 1989
3.4 CLOCKING OPTIONS
This section describes the transmit and receive clocking options for the serial channels.
It applies to all four independently configurable serial channels.
3.4.1
Hardware Configurations
The SCC receive clock input pin, RTXC, is driven from line receivers which are connected
to the JK RT input (see Section 2.5). Therefore, the frequency of SCC pin RTXC is
determined by the external clock connected to the RXC/RT input pin. This clock input
signal will be referred to as RXC/RT in this section. The crystal oscillator feature of the
SCC is not used.
The SCC transmit clock pin, TRXC, is used as an output. It is buffered by line drivers
and driven to a TXC/TT output on a front edge connector. The SCC pin TRXC must be
programmed as an output (WRl 1) and must not be selected as an internal SCC clock source.
This clock output signal is referred to as TXC/TT in this section.
In all possible clocking combinations, the polarities of the clock signals TXC/TT and
RXC/RT are in accordance with the RS-232C or RS-485 standards.
The SCC’s clock pin PCLK is connected to a 3.6864 MHz clock. This frequency allows the
baud rate generator to produce most of the popular baud rates used for serial
communications.
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