z80189 ZiLOG Semiconductor, z80189 Datasheet - Page 159

• Manufacturer Part Number: z80189
• Description: Z80180, Z8s180, Z8l180 Mpu Operation
• Manufacturer: ZiLOG Semiconductor

144
UM005003-0703
Z8018x
Family MPU User Manual
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
else if BRG mode baud rate = f
else baud rate -f
The TC value for a given baud rate is:
TC = (f
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
0
0
1
1
PHI
DR
0
1
0
1
/*2*baud rate*Clock mode)) -2
Clock Mode
16
64
1
Reserved, do not use
PHI
/((10 + 20*PS) * 2^ss*Clock mode)
PHI
CKA
/(2*(TC+2)*Clock mode)
/Clock mode