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 47-13. Wait and guard time calculations
Parameter
Reset value
[ETU]
C7816[TTYPE] = 0
[ETU]
C7816[TTYPE] = 1
[ETU]
Wait time (WT) 9600 WI × 480 Not used
Character wait time (CWT) Not used Not used 2
(CWI1)
+ CWI2
Block wait time (BWT) Not used Not used (11 + (BWI × 960 × GTFD)) * (WTX
+ 1)
Guard time (GT) 12
GTN not equal to 255
12 + GTN
GTN equal 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 16 + BGI
NOTE
• User must ensure that the Character Wait time (CWT)
programmed using the formula above is atleast 12. Values
smaller than 12 are invalid and will lead to unexpected
CWT interrupts.
• The 16 bit Wait Time integer WI is formed by
concatenation of {WP7816A_T0[WI_H],
WP7816B_T0[WI_L]}.
• The 16 bit Block Wait Time integer BWI is formed by
concatenation of {WP7816A_T1[BWI_H],
WP7816B_T1[BWI_L]}.
Chapter 47 Universal Asynchronous Receiver/Transmitter (UART)
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors 1289
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