SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 68

• Manufacturer Part Number: SAB80C517-M16
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

On-Chip Peripheral Components
This condition flags the TX control unit to do one last shift and then deactivate SEND and set TI0/
TI1. This occurs at the 11th divide-by-16 rollover after "write-to-S0BUF/S1BUF".
Reception is initiated by a detected 1-to-0 transition at RxD0/RxD1. For this purpose RxD0/RxD1 is
sampled of a rate of 16 times whatever baud rate has been established. When a transition is
detected, the divide-by-16 counter is immediately reset, and 1F H is written to the input shift register.
At the 7th, 8th and 9th counter state of each bit time, the bit detector samples the value of RxD0/
RxD1. The value accepted is the value that was seen in at least 2 of the 3 samples. lf the value
accepted during the first bit time is not 0, the receive circuits are reset and the unit goes back to
looking for another 1-to-0 transition. lf the start bit proves valid, it is shifted into the input shift
register, and reception of the rest of the frame will proceed.
As data bits come from the right, 1’s shift out to the left. When the start bit arrives at the leftmost
position in the shift register (which is a 9-bit register), it flags the RX control block to do one last shift,
load S0BUF/S1BUF and RB80/ RB81, and set RI0/RI1. The signal to load S0BUF/S1BUF and
RB80/RB81, and to set RI0/RI1, will be generated if, and only if, the following conditions are met at
the time the final shift pulse is generated:
1) RI0/RI1 = 0, and
2) either SM20/SM21 = 0 or the received 9th data bit = 1
lf either one of these two conditions is not met, the received frame is irretrievably lost, and RI0/Rl1
is not set. lf both conditions are met, the received 9th data bit goes into RB80/RB81, the first 8 data
bits go into S0BUF/S1BUF. One bit time later, no matter whether the above conditions are met or
not, the unit goes back to look for a 1-to-0 transition at the RxD0/RxD1 input.
Note that the value of the received stop bit is irrelevant to S0BUF/S1BUF, RB80/RB81, or RI0/Rl1.
Semiconductor Group
69