TC1796
Peripheral Units (Vol. 2 of 2)
Asynchronous/Synchronous Serial Interface (ASC)
User’s Manual
19-6
V2.0, 2007-07
ASC, V2.0
9-Bit Data Frames
The 9-bit data frames consist of nine data bits D8 … D0 (CON.M = 100
B
), or of eight data
bits D7 … D0 plus an automatically generated parity bit (CON.M = 111
B
) or of eight data
bits D7 … D0 plus wake-up bit (CON.M = 101
B
). Parity may be odd or even, depending
on bit CON.ODD. An even parity bit will be set if the modulo-2-sum of the eight data bits
is 1. An odd parity bit will be cleared in this case. Parity checking is enabled via bit
CON.PEN (always OFF in 9-bit data and wake-up mode). The parity error flag CON.PE
will be set along with the error interrupt request flag if a wrong parity bit is received. The
received parity bit itself will be stored in RBUF too.
Figure 19-4 Asynchronous 9-Bit Frames
In Wake-up Mode (CON.M = 101
B
), received frames are transferred to the receive buffer
register only if the 9
th
bit (the wake-up bit) of the frame is 1. If this bit is 0, no receive
interrupt request will be activated and no data will be transferred.
This feature can be used to control communication in multi-processor systems, for
example.
When the master processor aims to transmit a block of data to one of several slaves, it
first sends out an address ‘byte’ (in this case, a ‘byte’ consists of nine bits) that identifies
the target slave. An address ‘byte’ differs from a data ‘byte’ in that the additional 9
th
bit is
a 1 for an address ‘byte’ but is a 0 for a data ‘byte’, so, no slave will be interrupted by a
data ‘byte’. An address ‘byte’ will interrupt all slaves (operating in 8-bit data + wake-up
bit mode), so each slave can examine the eight LSBs of the received character (the
address). The addressed slave will switch to 9-bit data mode (for example, by clearing
bit CON.M[0]), which enables it to also receive the data bytes that will be coming (having
the wake-up bit cleared). The slaves that were not being addressed remain in 8-bit data
+ wake-up bit mode, ignoring the following data ‘bytes’.
1
1
MCT05765
D5
D0
LSB
D3
D1
D2
D4
D7
D6
Start
Bit
0
(1st)
Stop
Bit
(2nd)
Stop
Bit
11-/12-Bit UART Frame
9 Data Bits
Bit 9
CON.M = 100
B
: Bit 9 = Data Bit D8
CON.M = 101
B
: Bit 9 = Wake-up Bit
CON.M = 111
B
: Bit 9 = Parity Bit