
DS26518 8-Port T1/E1/J1 Transceiver 
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NAME 
PIN 
TYPE 
FUNCTION 
WRB
/ 
RWB
R7 
Input 
Write-Read Bar/Read-Write Bar. 
This active-low signal along with 
CSB
 qualifies 
write access to one of the DS26518 registers. Data at D[7:0] is written into the 
addressed register at the rising edge of 
WRB 
while
 CSB
 is low. 
Interrupt Bar. 
This active-low output is asserted when an unmasked interrupt 
event is detected. 
INTB
 will be deasserted (and tri-stated) when all interrupts 
have been acknowledged and serviced. Extensive mask bits are provided at the 
global level, framer, LIU, and BERT level. 
SPI Serial Bus Mode Select/Analog Loss/Receive Signaling Freeze/Framer 
LOS 
INTB 
R9 
Output, 
Tri-
Stateable 
SPI_SEL/ 
AL/RSIGF/FLOS1 
C3 
Input with 
internal 
pulldown/ 
Output 
SPI_SEL: 
0 = Parallel Bus Mode, 1 = SPI Serial Bus Mode 
AL/RSIGF/FLOS1: 
Analog LOS reflects the loss of signal detected by the LIU 
front-end; framer LOS is LOS detection by the corresponding framer. The same 
pins can reflect receive-signaling freeze indications. This selection can be made 
by settings in Global Transceiver Control Register (
GTCR1
). AL/RSIGF/FLOS1 
are available by setting the 
GTCR1
.528MD bit to 1.
Bus Type Select. 
Set high to select Motorola bus timing, low to select Intel bus 
timing. This pin controls the function of the 
RDB/DSB
 and 
WRB
 pins. 
Note:
 If SPI 
mode is selected by the SPI_SEL pin, this pin must be tied low.
SYSTEM INTERFACE 
Master Clock. 
This is an independent free-running clock whose input can be a 
multiple of 2.048MHz ±50ppm or 1.544MHz ±50ppm. The clock selection is 
available by bits MPS0 and MPS1 and FREQSEL. Multiple of 2.048MHz can be 
internally adapted to 1.544MHz. Multiple of 1.544MHz can be adapted to 
2.048MHz. Note that TCLKn must be 2.048MHz for E1 and 1.544MHz for T1/J1 
operation. See 
Table 10-12
. 
Reset Bar. 
Active-low reset. This input forces the complete DS26518 reset. This 
includes reset of the registers, framers, and LIUs. 
Reference Clock Input/Output 
Input:
A 2.048MHz or 1.544MHz clock input. This clock can be used to generate 
the backplane clock. This allows for the users to synchronize the system 
backplane with the reference clock. The other options for the backplane clock 
reference are LIU-received clocks or MCLK. 
Output:
This signal can also be used to output a 1.544MHz or 2.048MHz 
reference clock. This allows for multiple DS26518s to share the same reference 
for generation of the backplane clock. Hence, in a system consisting of multiple 
DS26518s, one can be a master and others a slave using the same reference 
clock. 
TEST 
BTS 
M13 
Input 
MCLK 
B7 
Input 
RESETB 
J12 
Input 
REFCLKIO 
A7 
Input/ 
Output 
DIGIOEN 
D8 
Input, 
Pullup 
Digital Enable. 
When this pin and 
JTRST
 are pulled low, all digital I/O pins are 
placed in a high-impedance state. If this pin is high the digital I/O pins operate 
normally. This pin must be connected to V
DD
 for normal operation. 
JTRST 
L5 
Input, 
Pullup 
JTAG Reset. 
JTRST
 is used to asynchronously reset the test access port 
controller. After power-up, 
JTRST
 must be toggled from low to high. This action 
sets the device into the JTAG DEVICE ID mode. Pulling 
JTRST
 low restores 
normal device operation. 
JTRST
 is pulled high internally via a 10k
Ω
 resistor 
operation. If boundary scan is not used, this pin should be held low. 
JTAG Mode Select. 
This pin is sampled on the rising edge of JTCLK and is used 
to place the test access port into the various defined IEEE 1149.1 states. This pin 
has a 10k
Ω
 pullup resistor. 
JTAG Clock. 
This signal is used to shift data into JTDI on the rising edge and out 
of JTDO on the falling edge.  
JTAG Data In. 
Test instructions and data are clocked into this pin on the rising 
edge of JTCLK. This pin has a 10k
Ω
 pullup resistor. 
JTMS 
K4 
Input, 
Pullup 
JTCLK 
F5 
Input 
JTDI 
H4 
Input, 
Pullup 
Output, 
High 
Impedance 
JTDO 
J4 
JTAG Data Out. 
Test instructions and data are clocked out of this pin on the 
falling edge of JTCLK. If not used, this pin should be left unconnected.