
Electrical Characteristics
6-36
MC68302 USER’S MANUAL
MOTOROLA
6.22 AC ELECTRICAL SPECIFICATIONS—NMSI TIMING
The NMSI mode uses two clocks
,
one for receive and one for transmit. Both clocks can be
internal or external. When t he clock is internal
,
it is generated by the internal baud rate gen-
erator and it is output on TCLK or RCLK. All the timing is related to the external clock pin.
The timing is specified for NMSI1. It is also valid for NMSI2 and NMSI3 (see Figure 6-24).
NOTES:
1. The ratio CLKO/TCLK1 and CLKO/RCLK1 must be greater than or equal to 2.5/1 for external clock. The input clock
to the baud rate generator may be either an internal clock or TIN1, and may be as fast as EXTAL. However, the
output of the baud rate generator must provide a CLKO/TCLK1 and CLKO/RCLK1 ratio greater than or equal to 3/1.
In asynchronous mode (UART), the bit rate is 1/16 of the TCLK1/RCLK1 clock rate.
2. Also applies to CD hold time when CD is used as an external sync in BISYNC or totally transparent mode.
3. Schmitt triggers used on input buffers.
4. Where P = 1/CLKO. Thus, for a 16.67-MHz CLKO rate, P = 60 ns.
16.67 MHz 16.67 MHz
20 MHz
20 MHz
25 MHz
25 MHz
Num.
Characteristic
Internal
Clock
External
Clock
Internal
Clock
External
Clock
Internal
Clock
External
Clock
Unit
Min
Max
Min
Max
Min
Max
Min
Max
Min
Max
Min
Max
315
RCLK1 and TCLK1 Fre-
quency (see Note 1)
RCLK1 and TCLK1 Low
(see Note 4)
RCLK1 and TCLK1 High
RCLK1 and TCLK1 Rise/Fall
Time (see Note 3)
TXD1 Active Delay from
TCLK1 Falling Edge
RTS1 Active/Inactive Delay
from TCLK1 Falling Edge
CTS1 Setup Time to TCLK1
Rising Edge
RXD1 Setup Time to RCLK1
Rising Edge
RXD1 Hold Time from
RCLK1 Rising Edge (see
Note 2)
CD1 Setup Time to RCLK1
Rising Edge
—
5.55
—
6.668
—
6.66
—
8
—
8.33
—
10
MHz
316
65
—
P+10
—
55
—
P+10
—
45
—
P+10
—
ns
316a
65
—
55
—
55
—
45
—
45
—
35
—
ns
317
—
20
—
—
—
17
—
—
—
14
—
—
ns
318
0
40
0
70
0
30
0
50
0
25
0
40
ns
319
0
40
0
100
0
30
0
80
0
25
0
65
ns
320
50
—
10
—
40
—
7
—
35
—
7
—
ns
321
50
—
10
—
40
—
7
—
35
—
7
—
ns
322
10
—
50
—
7
—
40
—
7
—
35
—
ns
323
50
—
10
—
40
—
7
—
35
—
7
—
ns