Information

transmission or reception. Block guard time (BGT) is the minimum allowable time
between the leading edges of two consecutive characters in opposite directions, that is,
transmission then reception or reception then transmission.
The GT and WT counters reset whenever C7816[TTYPE] = 1 or C7816[ISO_7816E] = 0
or a new dataword start bit has been received or transmitted as specified by the counter
descriptions. The CWT, CGT, BWT, BGT counters reset whenever C7816[TTYPE] = 0
or C7816[ISO_7816E] = 0 or a new dataword start bit is received or transmitted as
specified by the counter descriptions. When C7816[TTYPE] = 1, some of the counter
values require an assumption regarding the first data transferred when the UART first
starts. This assumption is required when the 7816E is disabled, when transition from
C7816[TTYPE] = 0 to C7816[TTYPE] = 1 or when coming out of reset. In this case, it is
assumed that the previous non-existent transfer was a received transfer.
The UART will automatically handle GT, CGT, and BGT such that the UART will not
send a packet before the corresponding guard time expiring.
Table 45-209. Wait and guard time calculations
Parameter
Reset value
[ETU]
C7816[TTYPE] = 0
[ETU]
C7816[TTYPE] = 1
[ETU]
Wait time (WT) 9600 WI × 960 × GTFD Not used
Character wait time (CWT) Not used Not used 11 + 2
CWI
Block wait time (BWT) Not used Not used 11 + 2
BWI
× 960 × GTFD
Guard time (GT) 12 GTN not wqual to 255
12 + GTN
GTN wqual to 255
12
Not used
Character guard time (CGT) Not used Not used GTN not equal to 255
12 + GTN
GTN equal to 255
11
Block guard time (BGT) Not used Not used 22
45.4.8.5 Baud rate generation
The value in WF7816[GTFD] does not impact the clock frequency. SBR and BRFD are
used to generate the clock frequency. This clock frequency is used by the UART only and
is not seen by the smartcard device. The transmitter clocks operates at 1/16 the frequency
of the receive clock so that the receiver is able to sample the received value 16 times
during the ETU.
Functional description
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
1132 Freescale Semiconductor, Inc.