SN8P2977
8-Bit Micro-Controller with Regulator, PGIA, 24-bit ADC
SONiX TECHNOLOGY CO., LTD
Page 88
Version 1.7
9.4 ABNORMAL POCKET
The abnormal pocket occurs in UART RX mode. Break pocket is one abnormal pocket of the UART architecture. The
abnormal pocket includes Stream period error, start bit error, stop bit error…When UART receives abnormal pocket,
the UFMER bit will be set “1”, and UART issues URXIRQ. The system finds the abnormal pocket through firmware.
UART changes to initial status until detecting next start bit.
bit0
bit1
bit2
bit3
bit4
bit5
bit6
bit7
Start
Stop
P
URX Pin
Start bit is error.
UART check the start bit is error and issue UFMER flag, but the UART still finishes receiving the pocket.
bit0
bit1
bit2
bit3
bit4
bit5
bit6
bit7
Start
Stop
P
URX Pin
Start bit is error.
UART check the stop bit is error and issue UFMER flag, but the UART still finishes receiving the pocket.
b
0
Start
UART RX
Processor
b
1
b
2
b
3
b
4
b
5
b
6
b
7
p
Stop
bit0
bit1
bit2
bit3
bit4
bit5
bit6
URX Pin
Start
If the host’s UART baud rate isn’t match to receiver terminal, the received pocket is error. But it is not easy to
differentiate the pocket is correct or not, because the received error pocket maybe match UART rule, but the data is
error. Use checking UFMER bit and URXPC bit status to decide the stream. If the two conditions seem like correct, but
the pocket is abnormal, UART will accept the pocket as correct one.
9.5 UART BAUD RATE
UART clock is 2-stage structure including a pre-scaler and an 8-bit buffer. UART clock source is generated from
system oscillator called Fhosc. Fhosc passes through UART pre-scaler to get UART main clock called Fuart. UART
pre-scaler has 8 selections (Fhosc/1, Fhosc/2, Fhosc/4, Fhosc/8, Fhosc/16, Fhosc/32, Fhosc/64, Fhosc/128) and 3-bit
control bits (URS[2:0]). UART main clock (Fuart) purposes are the front-end clock and through UART 8-bit buffer
(URCR) to obtain UART processing clock and decide UART baud rate.
UART Pre-scaler
Selection, URS[2:0]
UART Main Clock Rate
Fuart (Fhosc=8Hz)
000b
Fhosc/1
8MHz
001b
Fhosc/2
4MHz
010b
Fhosc/4
2MHz
011b
Fhosc/8
1MHz
100b
Fhosc/16
0.5MHz
101b
Fhosc/32
0.25MHz
110b
Fhosc/64
0.125MHz
111b
Fhosc/128
0.625MHz