AMD Am79C930 - Manual (Page 116)

AMD P R E L I M I N A R Y
116 Am79C930
edge baud counter. This information should be used to appropri-
ately program the Baud Detect Upper Limit register.
The resolution of the value in this register is the period of the CLKIN
signal when the CLKGT20 bit of MIR9 is set to 0 or twice the period
of the CLKIN signal when the CLKGT20 bit of MIR9 is set to 1. With
CLKIN = 20 MHz and CLKGT20=0, a value of 14h (=20 decimal)
represents the
nominal like transition separation value for a 1Mbit/s
network data rate.
TCR19: Baud Detect Accept Count for Carrier Sense
This register is the Baud Detect Accept Count for Carrier
Sense register. When the number of positive baud de-
tect test results in the baud detection circuit reaches the
value in this register, then the total number of tests taken to that point will be considered adequate to make a valid
determination of positive carrier sense. The number of
positive baud detect test results is reset to 0 each time
that the antenna selection is changed.
CONFIGURATION REGISTER INDEX: 13h
Bit Name Reset Value Description
7–6 Reserved – Reserved. Must be written as a 0. Reads of this bit produce
undefined data.
5–0 BDCS[5:0] 00h Baud Detect accept count for Carrier Sense. When the number of
positive baud detect test results in the baud detection circuit
reaches the value in this register, then the total number of tests
taken to that point will be considered adequate to make a valid de-
termination of positive carrier sense. The number of positive baud
detect test results is reset to 0 each time that the antenna selection
is changed.
TCR20: Baud Detect Accept Count for Stop Diversity
This register is the Baud Detect Accept Count for Stop
Diversity register. When the number of positive baud de-
tect test results in the baud detection circuit reaches the
value in this register, then the total number of tests taken to that point will be considered adequate to make a valid
determination of satisfactory antenna selection. The
number of positive baud detect test results is reset to 0
each time that the antenna selection is changed.
CONFIGURATION REGISTER INDEX: 14h
Bit Name Reset Value Description
7–6 Reserved – Reserved. Must be written as a 0. Reads of this bit produce unde-
fined data.
5–0 BDSD[5:0] 00h Baud Detect accept count for Stop Diversity. When the number of
positive baud detect test results in the baud detection circuit
reaches the value in this register, then the total number of tests
taken to that point will be considered adequate to make a valid de-
termination of satisfactory antenna selection. The number of posi-
tive baud detect test results is reset to 0 each time that the antenna
selection is changed.
TCR21: Baud Detect Ratio
This register is the Baud Detect Ratio register. This reg-
ister is used to set the ratio of good to bad baud detec-
tions which will be used as the minimum ratio to
determine that a valid signal is present on the medium. The value in this register is treated as a radix 2 positive
real number with two decimal places. The lowest practi-
cal value possible is 0.25 (=00.01) and the highest prac-
tical value is 3.75 (=11.11).