Intel 386 - Manual (Page 404)

13-5
SYNCHRONOUS SERIAL I/O UNIT
13.2 SSIO OPERATION
The following sections describe the operation of the baud-rate generator, transmitter, and receiv-
er.
13.2.1 Baud-rate Generator
Either the prescaled clock or the serial clock (PSCLK or SERCLK) can drive the baud-rate gen-
erator (Figure 13-5). The SIO and SSIO configuration register (SIOCFG) selects one of these
sources.
Figure 13-5. Clock Sources for the Baud-rate Generator
OR
SERCLK provides a baud-rate input frequency (BCLKIN) of CLK2/4. The PSCLK frequency
depends on the 9-bit programmable divider. The input to the programmable divider is divided by
a 9-bit prescale value + 2.
A prescale value of 0 gives the maximum PSCLK frequency (CLK2/4) and a prescale value of
1FFH (511) gives the minimum PSCLK frequency (CLK2/1026).
A2443-02
1
0
Baud-rate
Generator
BCLKIN
ч 2 ч 2
9-bit Programmable Divider
CLK2
SERCLK
PSCLK
SIOCFG.2
CLKPRS
SSIOBAUD
BV6:0
BCL KIN SERCLK
C LK 2
4
---------------- = =
B C LKIN PSC LK
CLK2/2
prescale value 2 +
------------------------------------------------ = =