STANDARD PRODUCT
PM4351 COMET
DATA SHEET
PMC-1970624
ISSUE 10
COMBINED E1/T1 TRANSCEIVER
enable for the data bus. While the DBCTRL bit is set, holding the CSB pin
high causes the COMET to drive the data bus and holding the CSB pin low
tri-states the data bus. The DBCTRL bit overrides the HIZDATA bit. The
DBCTRL bit only has effect when the IOTST or PMCTST bit is set to logic 1.
The DBCTRL bit is used to measure the drive capability of the data bus driver
pads.
IOTST:
The IOTST bit is used to allow normal microprocessor access to the test
registers and control the test mode in each block in the COMET for board
level testing. When IOTST is a logic 1, all blocks are held in test mode and
the microprocessor may write to a block's test mode 0 registers to manipulate
the outputs of the block and consequently the device outputs (refer to the
"Test Mode 0 Details" in the "Test Features" section).
HIZIO, HIZDATA:
The HIZIO and HIZDATA bits control the tri-state modes of the COMET .
While the HIZIO bit is a logic 1, all output pins of the COMET except the data
bus are held in a high-impedance state. The microprocessor interface is still
active. While the HIZDATA bit is a logic 1, the data bus is also held in a high-
impedance state which inhibits microprocessor read cycles.
PROPRIETARY AND CONFIDENTIAL
101
PMC [ PMC-SIERRA, INC ]
