mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 1123

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

Chapter 43 Universal Asynchronous Receiver/Transmitter (UART)
ISO 7816 FORMAT (T=1)
NEXT
PARITY
START
START
STOP
BIT
BIT
BIT 0
BIT 1
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BIT
BIT
Figure 43-117. ISO 7816 T=1 data format
The smallest data unit that is transferred is a block. A block is made up of several data
characters and may vary in size depending on the block type. The UART does not
provide a mechanism to decode the block type. As part of the block, an LRC or CRC is
included. The UART does not calculate the CRC or LRC for transmitted blocks nor does
it verify the validity of the CRC or LRC for received blocks. The 7816 protocol requires
that the initiator and the smartcard (device) takes alternate turns in transmitting and
receiving blocks. When the UART detects that the last character in a block has been
transmitted it will automatically clear the C2[TE] bit and enter receive mode. Hence,
software must program the transmit buffer with the next data to be transmitted and then
enable the C2[TE] bit once software has determined that the last character of the received
block has been received. The UART detects that the last character of the transmit block
has been sent when TL7816[TLEN] = 0 and four additional characters have been sent.
The four additional characters are made up of three prior to TL7816[TLEN]
decrementing (prologue) and one after TL7816[TLEN] = 0, the final character of the
epilogue.
43.4.7.4 Wait time and guard time parameters
The ISO-7816 specification defines several wait time and guard time parameters. The
UART allows for flexible configuration and violation detection of these settings. On reset
the wait time (IS7816[WT]) defaults to 9600 ETUs and guard time (GT) to 12 ETUs.
These values are controlled by parameters in the WP7816, WN7816 and WF7816
registers. Additionally the value of C7816[TTYPE] also factors into the calculation. The
formulas used to calculate the number ETU for each wait time and guard time value are
shown in the following table.
Wait time (WT) is defined as the maximum allowable time between the leading edge of a
character transmitted by the device (smartcard) and the leading edge of the previous
character that was transmitted by the UART or the device. Likewise character wait time
(CWT) is defined as the maximum allowable time between the leading edge of two
characters within the same block, and block wait time (BWT) is defined as the maximum
time between the leading edge character of the last block received by the device/
smartcard and the leading edge of the first character transmitted by the device/smartcard.
Guard time (GT) is defined as the minimum allowable time between the leading edge of
two consecutive characters. Character guard time (CGT) is the minimum allowable time
between the leading edges of two consecutive characters in the same direction
MCF51JF128 Reference Manual, Rev. 2, 03/2011
Preliminary
Freescale Semiconductor, Inc.
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