# Asynchronous Operational Range

The operational range of the receiver is dependent on the mismatch between the received bit rate and the internally generated baud rate. If an external transmitter is sending using bit rates that are too fast or too slow, or if the internally generated baud rate of the receiver does not match the external source’s base frequency, the receiver will not be able to synchronize the frames to the start bit.

The following equations can be used to calculate the ratio of the incoming data rate and internal receiver baud rate.

 RSLOW=16(D+1)16(D+1)+6 RFAST=16(D+2)16(D+1)+8

D Sum of character size and parity size (D = 5 to 10 bit).

Rslow Is the ratio of the slowest incoming data rate that can be accepted in relation to the receiver baud rate.

Rfast Is the ratio of the fastest incoming data rate that can be accepted in relation to the receiver baud rate.

The following tables list the maximum receiver baud rate error that can be tolerated. Normal Speed mode has higher toleration of baud rate variations.

Table 1. Recommended Maximum Receiver Baud Rate Error for Normal Speed Mode (CLK2X = 0)
D #(Data + Parity bit) Rslow [%] Rfast [%] Maximum total error [%] Receiver max. receiver error [%]
5 93.20 106.67 +6.67/-6.80 ±3.0
6 94.12 105.79 +5.79/-5.88 ±2.5
7 94.81 105.11 +5.11/-5.19 ±2.0
8 95.36 104.58 +4.58/-4.54 ±2.0
9 95.81 104.14 +4.14/-4.19 ±1.5
10 96.17 103.78 +3.78/-3.83 ±1.5
Table 2. Recommended Maximum Receiver Baud Rate Error for Double Speed Mode (CLK2X = 1)
D #(Data + Parity bit) Rslow [%] Rfast [%] Maximum total error [%] Receiver max. receiver error [%]
5 94.12 105.66 +5.66/-5.88 ±2.5
6 94.92 104.92 +4.92/-5.08 ±2.0
7 95.52 104.35 +4.35/-4.48 ±1.5
8 96.00 103.90 +3.90/-4.00 ±1.5
9 96.39 103.53 +3.53/-3.61 ±1.5
10 96.70 103.23 +3.23/-3.30 ±1.0

The recommendations of the maximum receiver baud rate error were made under the assumption that the receiver and transmitter equally divide the maximum total error.