
19 UART 1
S1C38000 TECHNICAL MANUAL
EPSON
177
19 UART 1
19.1 Overview
The channel one UART (UART1) is fully compatible with the industry-standard 16550. It converts
data from parallel to serial (from CPU to peripheral device) and serial to parallel (from peripheral
device to CPU). It supports the RTS/CTS port for modem control, and supports interrupt and DMA
requests. UART1 uses a fixed 24 MHz clock input for the baud rate generator.
19.2 Register Descriptions
The default base address for the UART1 registers is F8000400h. All non-reserved register bits
default to 0 unless specified otherwise.
All UART register accesses must be 8-bit.
bits 7–0
Receive Buffer Bits [7:0]
When the DLAB bit in the Line Control Register is 0, this read-only register contains
the data byte transmitted to the serial port. The data in this register is valid only if the
Data Ready bit in the Line Status Register is 1. This register accesses the head of the
receive FIFO. If the receive FIFO is full, the data already in the FIFO will be preserved,
but any incoming data will be lost.
bits 7–0
Transmit Holding Bits [7:0]
When the DLAB bit in the Line Control Register is 0, this write-only register contains
the data byte to be transmitted from the serial port. Up to 16 bytes of data may be
written to this register before the FIFO is full, after which any attempt to write data
results in the write data being lost.
bits 7–0
Divisor Latch LSB Bits [7:0]
When the DLAB bit in the Line Control Register is 1, these bits form the LSB of a 16-
bit Divisor Latch register that contains the baud rate divisor for the UART. The output
baud rate is:
baud rate = (24 MHz) / (16 x (URT1[04h], URT1[00h]))
Receive Buffer Register
URT1[00h]
DLAB[0]
Default = 0000 0000h
Read Only
n/a
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
n/a
Receive Buffer
15
14
13
12
11
10
9876543210
Transmit Holding Register
URT1[00h]
DLAB[0]
Write Only
n/a
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
n/a
Transmit Holding
15
14
13
12
11
10
9876543210
Divisor Latch LSB Register
URT1[00h]
DLAB[1]
Default = 0000 0000h
Read/Write
n/a
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
n/a
Divisor Latch LSB
15
14
13
12
11
10
9876543210