Zilog Z80180 - Manual (Page 159)

Z8018x
Family MPU User Manual
144
UM005003-0703
a common baud rate of up to 512 Kbps to be selected. The BRG can also
be disabled in favor of an external clock on the CKA pin.
The Receiver and Transmitter subsequently divide the output of the BRG
(or the signal from the CKA pin) by 1, 16, or 64, under the control of the
DR bit in the CNTLB register, and the X1 bit in the ASCI Extension
Control REgister. To compute baud rate, use the following formulas:
Where:
BRG mode is bit 3 of the ASEXT register
PS is bit 5 of the CNTLB register
TC is the 16-bit value in the ASCI Time Constant register
If ss2.1.0 = 111, baud rate - f
CKA
/Clock mode
else if BRG mode baud rate = f PHI /(2*(TC+2)*Clock mode)
else baud rate -f PHI /((10 + 20*PS) * 2^ss*Clock mode)
The TC value for a given baud rate is:
TC = (f PHI /*2*baud rate*Clock mode)) -2
Clock mode depends on bit 4 in ASEXT and bit 3 in CNTLB, as
described in Table 20.
Table 20. Clock Mode Bit Values
X1 DR Clock Mode
0
0
1
1 0
1
0
1 16
64
1
Reserved, do not use