LFDAS12XSDT Freescale Semiconductor, LFDAS12XSDT Datasheet - Page 182

• Manufacturer Part Number: LFDAS12XSDT
• Description: HARDWARE MC9S12XS 52-PIN
• Manufacturer: Freescale Semiconductor

Specifications of LFDAS12XSDT

• Module/board Type: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: -

Background Debug Module (S12XBDMV2)
The timing for host-to-target is shown in
Figure
the host and target are operating from separate clocks, it can take the target system up to one full clock
cycle to recognize this edge. The target measures delays from this perceived start of the bit time while the
host measures delays from the point it actually drove BKGD low to start the bit up to one target clock cycle
earlier. Synchronization between the host and target is established in this manner at the start of every bit
time.
Figure 5-8
target system. The host is asynchronous to the target, so there is up to a one clock-cycle delay from the
host-generated falling edge to where the target recognizes this edge as the beginning of the bit time. Ten
target clock cycles later, the target senses the bit level on the BKGD pin. Internal glitch detect logic
requires the pin be driven high no later that eight target clock cycles after the falling edge for a logic 1
transmission.
Since the host drives the high speedup pulses in these two cases, the rising edges look like digitally driven
signals.
The receive cases are more complicated.
system. Since the host is asynchronous to the target, there is up to one clock-cycle delay from the host-
generated falling edge on BKGD to the perceived start of the bit time in the target. The host holds the
BKGD pin low long enough for the target to recognize it (at least two target clock cycles). The host must
release the low drive before the target drives a brief high speedup pulse seven target clock cycles after the
perceived start of the bit time. The host should sample the bit level about 10 target clock cycles after it
started the bit time.
182
Start of Bit Time
(Target MCU)
BDM Clock
Transmit 1
Transmit 0
5-10. All four cases begin when the host drives the BKGD pin low to generate a falling edge. Since
Perceived
shows an external host transmitting a logic 1 and transmitting a logic 0 to the BKGD pin of a
Host
Host
Synchronization
Uncertainty
Figure 5-8. BDM Host-to-Target Serial Bit Timing
S12XS Family Reference Manual, Rev. 1.11
Figure 5-9
Figure 5-8
10 Cycles
shows the host receiving a logic 1 from the target
and that of target-to-host in
Target Senses Bit
Figure 5-9
Freescale Semiconductor
and
Next Bit
Earliest
Start of