Serial Ports
12-18
Figure 12–13. Serial-Port Global-Control Register
28
RRESET
RTINT
XINT
XTINT
31
30
29
27
26
25
24
23
22
21
20
19
18
17
16
RLEN
XLEN
FSRP
FSXP
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
CLKXP
RFSM
XFSM
RCLK
XCLK
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
HS
RSR
XSR
FSXOUT
XRDY
RRDY
SRCE
SRCE
FULL
EMPTY
R/W
R/W
R/W
R/W
R/W
R/W
R
R
R/W
R
R
XRESET
RINT
R/W
DRP
DXP
CLKRP
RVAREN
XVAREN
R/W
R/W
R/W
R/W
R/W
xx
xx
xx
xx
Notes:
1) R = read, W = write
2) xx = reserved bit, read as 0
Table 12–2. Serial-Port Global-Control Register Bits Summary
Abbreviation
Reset
Value
Name
Description
RRDY
0
Receive ready flag
If RRDY = 1, the receive buffer has new data and is ready to
be read. A three H1/H3 cycle delay occurs from the loading
of DRR to RRDY = 1. The rising edge of this signal sets RINT.
If RRDY = 0, the receive buffer does not have new data since
the last read. RRDY = 0 at reset and after the receive buffer is
read.
XRDY
1
Transmit ready flag
If XRDY = 1, the transmit buffer has written the last bit of data
to the shifter and is ready for a new word. A three H1/H3 cycle
delay occurs from the loading of the transmit shifter until
XRDY is set to 1. The rising edge of this signal sets XINT.
If XRDY = 0, the transmit buffer has not written the last bit of
data to the transmit shifter and is not ready for a new word.
FSXOUT
Transmit frame sync
configuration
FSXOUT = 0 configures the FSX pin as an input.
FSXOUT = 1 configures the FSX pin as an output.
XSREMPTY
0
Transmit-shift
register empty flag
If XSREMPTY = 0, the transmit-shift register is empty.
If XSREMPTY = 1, the transmit-shift register is not empty.
Reset or XRESET causes this bit to = 0.
RSRFULL
0
Receive-shift register
full flag
If RSRFULL = 1, an overrun of the receiver has occurred. In
continuous mode, RSRFULL is set to 1 when both RSR and
DRR are full. In noncontinuous mode, RSRFULL is set to 1
when RSR and DRR are full and a new FSR is received. A read
causes this bit to be set to 0. This bit can be set to 0 only by a
system reset, a serial-port receive reset (RRESET = 1), or a
read. When the receiver tries to set RSRFULL to 1 at the same
time that the global register is read, the receiver dominates,
and RSRFULL is set to 1.
If RSRFULL = 0, no overrun of the receiver has occurred.