Syslinux - May 2019 - Serial output does not work

Hello,

in my syslx64.cfg I have the line "serial 0 115200 0"
But if I  show the variable SerialPort, than the variable is zero.

We have a own c32 file. And with this I show (printf) the variable.
-------- our cfg file ------------------------
#
# EFI64 configuration
#

PATH x64
# Include does not work corret in this version
# INCLDUE /COMMON/common.cfg

CONSOLE 1

serial 0 115200 0

# 2017-11-07 obejoh: add threadirqs to activate threaded irqs
#
# Clear LEDs before starting Linux. After this salamander LABEL is called
internally.

# show screen
DISPLAY screen.lpg
# load plugin
DEFAULT hardware_init.c32

LABEL salamander
        KERNEL /bzImage
        APPEND root=/dev/sda2 rw nohlt idle=poll quiet xeno_hal.smi=1 isolcpus=0
irqaffinity=1 threadirqs

LABEL salamander_update
        KERNEL /bzImage
        INITRD /initramfs.igz
        APPEND root=/dev/ram init=/init

----------------------------------

Any idea, why serialport does not work ?

Thanks for help
  Regards
    Johann