Gopel Electronic SFX-TAP2/C, Техническое описание

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Desktop Transceiver SFX-TAP4_2/C, V0.1, Technical Description 23
t
delay
+ ∆ t + ∆ t - ∆ t - ∆ t
TCK
TDO
t
delay
T
TCK
f
TCK
= 1 / T
TCK
TDO mit ∆ t
Figure 14: Timing diagram for UUT TCK-TDO delay
The delay time
Delay
(t
delay
) to be entered is the elapsing time between falling TCK edge on the
TAP/PIP connector of the SFX-TAP4 (SFX-TAP2) until arriving the UUT’s TDO response on the
same connector.
Note,
Delay
(t
delay
) covers both, time delay of the UUT and cable.
TCK TDO delay delta
(∆
t) is the tolerance of the time delay. The higher the wanted TCK
frequency is, the more precise
∆
t has to be. The software calculates the TCK frequency
following this formula:
F
TCK
<= 1 / (4 x (
∆
∆ ∆
∆
t + 2 ns))
Maximum values of
TCK TDO delay delta
(∆
t), in order to get a particular TCK frequency:
•
TCK 20 MHz --> max
TCK TDO delay delta
= 10 ns
•
TCK 30 MHz --> max
TCK TDO delay delta
= 6 ns
•
TCK 50 MHz --> max
TCK TDO delay delta
= 3 ns
•
TCK 80 MHz --> max
TCK TDO delay delta
= 1 ns
Figure 14 shows a window defined by +
∆
t and -
∆
t. Within this window the TDO is expected.
Due to the nature of Boundary Scan a rising edge must appear only after that window. The
timing difference must be in the minimum as the window itself in order to get an independence
from the time delay.
The conclusion is: The SW has to reduce the TCK frequency depending on
∆
t.